An energy harvesting system capable of reducing open circuit voltage sampling time

Abstract

The application discloses an energy collection system capable of reducing open-circuit voltage sampling time, comprising an MPPT sampling circuit, a ZCD sampling circuit and a multiplexed logic unit circuit; during open-circuit voltage sampling, a power stage is kept open, reverse inductive current is utilized to charge an input capacitor, and a previous open-circuit voltage is used as a preset value to realize a pre-charging process, thereby accelerating the overall open-circuit voltage acquisition time; in addition, the application adopts a digital ZCD circuit to effectively reduce the power consumption of the ZCD, and meanwhile, the digital information of the MPPT is combined with the multiplexed logic unit, thereby reducing the corresponding area.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of integrated circuits, and particularly relates to an energy collection system capable of reducing open-circuit voltage sampling time. BACKGROUND

[0002] With the development of modern smart grid, wireless sensor network has become the preferred technical solution for realizing power grid state monitoring, and can also play an important role in smart home, smart power metering, etc., therefore, wireless sensor technology has become a hot technology in the development process of smart grid. Wireless sensor network nodes are generally static and may be located in places difficult for people to reach, so it is very difficult to replace the batteries, and therefore, the energy management problem in the wireless sensor network node is the key to prolonging the application life and reducing the cost.

[0003] Enabling the energy collection function in the energy management system of the wireless sensor network node is an effective way to prolong the battery use time; the energy collection technology, also known as the energy harvesting technology, is a technology of collecting and converting the unused energy in the environment into directly usable electric energy, and the maximum power point collection and low-power module design will be two difficulties.

[0004] The output curve of the energy converter is nonlinear, and therefore, there is a specific maximum power point, and the MPPT (Maximum Power Point Tracking) circuit is to obtain the maximum power point voltage, and the common methods include the open-circuit voltage method, short-circuit current method and hill climbing method, etc. For the open-circuit voltage method, the MPPT first measures the open-circuit voltage by opening the DC end when tracking, and then calculates the maximum power voltage through an algorithm; the collection of the open-circuit voltage needs a long time when the energy is weak, and the system is in a dormant state in this process, which will waste a lot of energy. For the energy collection system, when the P tube is turned on, the system charges the output capacitor, and the inductor current decreases, in order to avoid the reverse discharge of the output capacitor due to the zero crossing of the inductor current, the ZCD (Zero Crossing Detector) circuit is needed to detect whether the inductor current is zero crossing, the output zero crossing signal is outputted after the output voltage and the SW (Switch) signal of the circuit are compared, and the comparator is an indispensable part, and the power consumption of this part is usually large.

[0005] The document [Bose.S, Anand.T, Johnston.M.L. "A 3.5-mV Input Single-Inductor Self-Starting Boost Converter With Loss-Aware MPPT for Efficient Autonomous Body-Heat Energy Harvesting" [J]. IEEE Journal of Solid-State Circuits, 2020, PP(99): 1-1] proposes the concept of digital ZCD, which expresses the output of ZCD in digital form and combines system loss with MPPT circuit efficiency to fix 16 groups of operating frequency and duty cycle in digital form, but the structure is relatively complex. The document [K. Kadirvel et al. "A 330nA energy-harvesting charger with battery management for solar and thermoelectric energy harvesting" in IEEE Int. Solid-State Circuits Conf. (ISSCC) Dig. Tech. Papers, Feb. 2012, pp. 106-108] adopts the traditional FOCV-MPPT method, and the open-circuit voltage sampling time is as high as hundreds of milliseconds, so the working period of MPPT has to be lengthened to adapt to the sampling time, thereby causing the loss of efficiency.

[0006] For the existing energy harvesting system, the input voltage requirement is getting lower and lower, and the working range requirement is getting larger and larger, so when the output power is low, the system power consumption and the open-circuit voltage sampling time are put forward to high requirements. SUMMARY

[0007] In view of the above, the present application provides an energy harvesting system capable of reducing the open-circuit voltage sampling time, which can greatly reduce the open-circuit voltage sampling time when tracking the maximum power point, and greatly reduce the power consumption of the ZCD module using digital circuit form. Since the outputs of MPPT and ZCD are digital signals, the logic unit can be reused to reduce the area.

[0008] An energy harvesting system capable of reducing the open-circuit voltage sampling time, comprising:

[0009] An energy conversion circuit for converting other forms of energy collection in the environment into electrical energy and achieving maximum power output;

[0010] MPPT circuit, for sampling the open circuit voltage of the energy conversion circuit, generating an MPPT voltage proportional to the open circuit voltage;

[0011] ZCD sampling circuit, for zero-cross detection of the SW node voltage in the energy conversion circuit, outputting a zero-cross signal;

[0012] logic control circuit, for providing switching control signals for the power tubes in the energy conversion circuit according to the MPPT voltage and the zero-cross signal through logic control.

[0013] Further, the energy conversion circuit comprises an energy converter, an input capacitor C IN , power tubes M N and M P , an inductor L and an output capacitor C OUT , wherein the energy converter is used for converting other forms of energy collection in the environment into direct current, the output end of which is connected with one end of C IN and one end of L to generate an input voltage V IN , the other end of C IN is grounded, and the other end of L is connected with the drain of M N and the drain of M P to serve as a SW node, the source of M N is grounded, the source of M P is connected with one end of capacitor C OUT , the other end of C OUT is grounded, and the gates of M N and M P are connected with switching control signals Φ1 and Φ2 provided by the logic control circuit respectively.

[0014] Further, when sampling the open circuit voltage, the energy conversion circuit keeps the power stage open, charges the input capacitor C IN by pre-charging to make the voltage close to the open circuit voltage, then closes the power stage, charges the input capacitor C IN slowly by the energy converter alone, and samples the input voltage V IN after maintaining for a period of time to make the input voltage reach the open circuit voltage.

[0015] Further, the MPPT circuit comprises an operational amplifier AMP, a comparator CMP, four resistors R1-R4, a capacitor C FOCV , a switching tube M NOC , a timer Timer and an enable signal generation module Enable, wherein the positive input end of AMP is connected with the MPPT voltage V OCO, the inverting input of the AMP is connected to one end of R1 and one end of R2, the other end of R1 is grounded, the output of the AMP is connected to the other end of R2 and the inverting input of the CMP, the non-inverting input of the CMP is connected to the input voltage V IN , the output of the CMP triggers the enable Timer and Enable, the Enable is used to provide an on signal to the gate of M NOC , the Timer is used to give the action time of the on signal of the Enable, the source of M NOC is grounded, the drain of M NOC is connected to one end of R3, the other end of R3 is connected to one end of R4 and one end of C FOCV , and generates the current MPPT voltage V MPPT , the other end of R4 is connected to the input voltage V IN , and the other end of C FOCV is grounded.

[0016] Further, the MPPT voltage V OCO is in proportional relationship with the open circuit voltage V OC measured in the last time, that is, V OCO =k*V OC , k is a proportional coefficient and satisfies 1+R2 / R1=1 / k.

[0017] Further, the ZCD sampling circuit is realized by a digital circuit, which is composed of a D flip-flop, the input of the D flip-flop is connected to the voltage V SW of the SW node, the clock is connected to the switch control signal Φ2, and the output generates the zero-crossing signal ZCD_D.

[0018] Further, after the inductor current I L crosses zero, the output ZCD_D of the D flip-flop is 0; when the inductor current I L does not cross zero, the output ZCD_D of the D flip-flop is 1, and I L is the current flowing through the inductor L.

[0019] Further, the logic control circuit includes a 6-bit arithmetic logic unit ALU (Arithmetic and Logic Unit), a comparator, and two D flip-flops D1 and D2, wherein the non-inverting input of the comparator is connected to the input voltage V IN , and the inverting input of the comparator is connected to the MPPT voltage V MPPTThe ALU receives the comparison signal CMP_D outputted by the comparator, the zero-crossing signal ZCD_D and the given clock signal CLK3, and outputs the switch control signals Φ1 and Φ2 through internal logic control; D1 is connected with the ALU and serves as a register of the switch control signal Φ1, and the clock end thereof is connected with the given clock signal CLK1, which is used for controlling the input and output of Φ1 by D1; D2 is connected with the ALU and serves as a register of the switch control signal Φ2, and the clock end thereof is connected with the given clock signal CLK2, which is used for controlling the input and output of Φ2 by D2.

[0020] Further, the clock signal CLK3 is used for controlling the logic operation in the ALU, and since the working periods of the MPPT circuit and the ZCD sampling circuit are different, the ALU processes the output results of the MPPT circuit and the D flip-flop D1 when CLK3 is at high level, and processes the output results of the ZCD sampling circuit and the D flip-flop D1 when CLK3 is at low level, so as to realize the multiplexing of the ALU.

[0021] Further, the high level time of the clock signals CLK2 and CLK3 is 0.5 μs, the periods of CLK2 and CLK3 are 1 μs and 8 μs respectively, and the clock signal CLK1 is the result after CLK3 is delayed for 100 ns.

[0022] Compared with the prior art, the energy collection system of the present application can effectively improve the time for collecting the open circuit voltage by the MPPT circuit, can avoid the use of the comparator by using the digital collection of ZCD, can reduce the power consumption, and can effectively reduce the area of the module by multiplexing the MPPT and ZCD results in the logic unit. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 Fig. 1 is a structural block diagram of the energy collection system of the present application.

[0024] Figure 2 Fig. 2 is a structural schematic diagram of the MPPT module.

[0025] Figure 3 Fig. 3 is a topology schematic diagram of the improved energy conversion circuit.

[0026] Figure 4 Fig. 4 is a timing schematic diagram of the sampling signal when the MPPT works.

[0027] Figure 5 Fig. 5 is a structural schematic diagram of the ZCD module.

[0028] Figure 6 Fig. 6 is a structural schematic diagram of the logic control module for multiplexing the MPPT and ZCD. DETAILED DESCRIPTION

[0029] To describe the present invention in more detail, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] like Figure 1 As shown, the energy harvesting system of the present invention, which can reduce the open-circuit voltage sampling time, includes an energy conversion circuit, an MPPT module, a ZCD module, and a multiplexed logic control module. Specifically: when sampling the open-circuit voltage, the MPPT module keeps the power stage circuit open, pre-charges the input capacitor to near the open-circuit voltage, then shuts down the power stage, maintains the open-circuit voltage charging for a period of time, and then samples. The ZCD module uses digital circuitry to represent the current zero-crossing information with digital states "0" and "1". The MPPT and ZCD output digital "0" or "1" according to the current state. Because their operating cycles are different, the logic control module can be reused. The MPPT module obtains V from the energy conversion circuit. IN V during road opening IN The open-circuit voltage is V, and the current MPPT voltage V is output according to the preset algorithm. MPPT The ZCD module obtains the voltage at point SW from the energy conversion circuit and outputs the current zero-crossing signal ZCD_D according to the preset sampling logic; the logic control module obtains the MPPT voltage V. MPPT After ZCD_D, the current power transistor control signals Ф1 and Ф2 are converted and output according to the preset algorithm.

[0031] like Figure 2 As shown, the MPPT module includes an amplifier AMP, a comparator CMP, four resistors R1, R2, R3, and R4, and a capacitor C. FOCV The module includes a timer and an enable signal generator. The positive input of the AMP is connected to the previously stored MPPT open-circuit voltage, the negative input is connected to R1 to ground, and to R2 to the output. The output of the AMP is connected to the negative input of the CMP. The voltage V across the input capacitor is... IN The positive input of CMP is connected to the positive input terminal. The output terminals of CMP are connected to the Timer and Enable modules respectively. The output of the Timer is connected to Enable, and the output of Enable is connected to M. NOC The gate terminal, M NOC The source is grounded, the drain is connected to R3, and R3 and R4 are connected to V. IN and M NOC A voltage divider is formed between the drain terminals, and a capacitor C is connected at the voltage divider point. FOCV The voltage at that point is V. FOCV .

[0032] The positive input terminal of the amplifier AMP is V OCO (V OCOThis is the MPPT voltage obtained from the previous MPPT sampling. Since MPPT is measured using the open-circuit voltage method, its value is V. OCO =k*V OC V OC (This is the open-circuit voltage obtained from the previous measurement). The negative input terminal is the feedback signal between the output and ground through the two resistors. Therefore, the output voltage can be written as V. OCO (1+R2 / R1), adjust the ratio of R2 to R1 to satisfy 1+R2 / R1=1 / k, then consider the current output voltage to be approximately the same as the previous open-circuit voltage. Since the interval between two MPPT tracking tests is very short compared to environmental changes, the change in open-circuit voltage between the two tests can be considered negligible. Therefore, connect the negative input of comparator CMP to the output of AMP, and the positive input to V. IN When V IN The CMP output flips when the voltage exceeds the previous open-circuit voltage.

[0033] Traditional MPPT open-circuit voltage method requires shutting down the power stage and waiting for the energy converter to reach C when measuring open-circuit voltage. IN Charging is necessary because the output current of the energy converter is typically only in the microamp range when the energy is weak, thus requiring a long charging time. Figure 3 As shown, the input capacitor C IN The charging current has I PV and I L I PV This refers to the output current of the energy converter, which is typically in the microampere range. L This is the inductor current, which can reach tens of milliamps during operation; before the CMP output flips, the power stage remains on while the ZCD module is off, resulting in a reverse inductor current -I. L For C IN Continue charging, I L Much greater than I PV It can quickly work with C. IN Charging begins; once charging is complete and the CMP cycle is complete, the Enable module and Timer are enabled. The Timer is maintained for a given time of 2ms, during which time is used for I... PV For C IN Slow charging, turn on M NOC The transistor obtains the MPPT voltage for the current cycle through a voltage divider formed by resistors R3 and R4. Subsequently, the timer is turned off, the Enable module is disabled, and V... FOCV Voltage exists in capacitor C FOCV middle.

[0034] To reduce the open-circuit voltage sampling time, in addition to the MPPT module mentioned above, some improvements are needed in the system's energy conversion circuit topology, such as... Figure 3As shown, the circuit includes an energy converter and an input capacitor C. IN Power transistor M N and M P Inductor L and output capacitor C OUT The output of the energy converter is connected to C. IN And to the left of L, C IN The other end is grounded, and the right side of L is connected to the SW terminal of the power transistor. M N The source drain is connected to SW and ground, and the gate terminal is connected to the drive signal Ф1, M. P The source and drain are connected to V respectively. OUT And SW, the gate terminal is connected to the drive signal Ф2.

[0035] like Figure 4 As shown, in working state I L There is a reverse current, therefore I IN When the MPPT module is working, this reverse current will be superimposed, causing V to... IN The voltage rises rapidly, and after reaching the previous open-circuit voltage, it enters a timing phase, which is driven by the energy converter's own current I. PV The method involves charging the battery, allowing it to rise slowly to the open-circuit voltage, and then sampling the voltage. This allows for the rapid acquisition of the open-circuit voltage.

[0036] like Figure 5 As shown, the ZCD module adopts a digital circuit form, including a D flip-flop, whose D terminal is connected to V. SW The CLK terminal is connected to CLK_HS, and the Q terminal is connected to ZCD_D; during one operating cycle of the system, the power transistor M... N After shutdown, the six-bit digital signal output by the ZCD module is used to control the power transistor M in the energy harvesting system. P The duration of the activation, M P The switching signal of the transistor (from low to high) is used as the rising edge of the D flip-flop to acquire the current voltage signal V. SW Due to the characteristics of inductor current, the digital signal of node SW is 0 after the inductor current crosses zero and 1 when the inductor current has not crossed zero. Therefore, ZCD_D can output the current inductor current zero-crossing information as a digital signal.

[0037] The outputs of the ZCD module and the MPPT module are related to V. IN The comparison results are always digital signals "0" or "1". When adjusting the system, multiple digital signals are needed to improve accuracy; therefore, a multi-bit logic unit is required to calculate the digital signals. For example... Figure 6 As shown, this invention proposes a logic control module for multiplexing the output results of ZCD and MPPT, which includes an ALU unit, two six-bit D flip-flops, and a comparator CMP, wherein the output V of the MPPT module... MPPTThe negative input of CMP is connected to V IN The positive input of CMP is connected to V The output of CMP, CMP_D, is connected to a 6-bit ALU, the output of ZCD, ZCD_D, is connected to the ALU, and the clock CLK3 is also connected to the ALU. The input and output signals of two 6-bit D flip-flops are connected to the ALU, and the clock of the two 6-bit D flip-flops is CLK1 and CLK2 respectively.

[0038] When the system is in working state, the maximum power point voltage V MPPT is compared with the input voltage V IN The digital result of the current comparison, CMP_D, is obtained after CMP, and is input to the 6-bit ALU. The module can dynamically adjust the 6-bit output according to the current comparison result. Similarly, the ZCD module can also output digital signal ZCD_D. The frequencies of the MPPT module and the ZCD module are different. CLK1 controls the reading of the 6-bit register of the MPPT, CLK2 controls the reading of the 6-bit register of the ZCD, and CLK3 is used to control the calculation of the ALU. When CLK3 is high, the ALU processes the result of the MPPT, and when CLK3 is low, the ALU processes the result of the ZCD. In this embodiment, the period of CLK2 is 1 μs, the period of CLK3 is 8 μs, the high level time of CLK3 is 0.5 μs, and CLK1 is the result of CLK3 delayed by 100 ns. In an 8 μs working period, the first 1 μs is used for the calculation of the MPPT signal. At this time, the ALU is used to process the result of CMP_D and the corresponding 6DFF_R. The last 7 μs is used to process the result of ZCD_D and the corresponding 6DFF_R. The high and low levels of CLK3 are used as the switching process, so as to realize the multiplexing of the ALU.

[0039] The above description of the embodiments is for the purpose of enabling and applying the present application to those of ordinary skill in the art. Those skilled in the art can easily make various modifications to the above embodiments, and apply the general principles described herein to other embodiments without creative labor. Therefore, the present application is not limited to the above embodiments, and any improvement and modification of the present application made by those skilled in the art based on the disclosure of the present application should be within the scope of protection of the present application.

Claims

1. An energy harvesting system capable of reducing open circuit voltage sampling time, characterized in that, The application relates to a maximum power point tracking (MPPT) circuit, comprising: an energy conversion circuit for converting other forms of energy collection in the environment into electric energy and realizing maximum power output; an MPPT circuit for sampling the open circuit voltage of the energy conversion circuit and generating an MPPT voltage in a certain proportional relationship with the open circuit voltage; a ZCD sampling circuit for zero-cross detection of the SW node voltage in the energy conversion circuit and outputting a zero-cross signal; a logic control circuit for providing a switching control signal for a power tube in the energy conversion circuit according to the MPPT voltage and the zero-cross signal through logic control; The energy conversion circuit comprises an energy converter, an input capacitor C IN , a power transistor M N , a transistor M P , an inductor L and an output capacitor C OUT , wherein the energy converter is used to convert the energy collection in other forms in the environment into direct current, the output end of the energy converter is connected with one end of C IN and one end of L to generate an input voltage V IN , the other end of C IN is grounded, the other end of L is connected with the drain of M N and the drain of M P to serve as a SW node, the source of M N is grounded, the source of M P is connected with one end of the capacitor C OUT , the other end of C OUT is grounded, and the gates of M N and M P are connected with switch control signals Φ1 and Φ2 provided by a logic control circuit respectively. At the time of sampling the open circuit voltage, the energy conversion circuit keeps the power stage open, the input capacitor C IN is charged by pre-charge to a voltage close to the open circuit voltage, then the power stage is closed and the input capacitor C IN is charged slowly by the energy converter alone, maintaining the input voltage V IN for a certain time until it reaches the open circuit voltage, which is then sampled. The MPPT circuit includes an operational amplifier AMP, a comparator CMP, four resistors R1 to R4, and a capacitor C. FOCV Switching transistor M NOC The Timer and Enable signal generation module are configured, with the non-inverting input of the AMP connected to the MPPT voltage V obtained from the previous sampling. OCO The inverting input of the AMP is connected to one end of R1 and one end of R2, and the other end of R1 is grounded. The output of the AMP is connected to the other end of R2 and the inverting input of the CMP. The non-inverting input of the CMP is connected to the input voltage V. IN The output of CMP triggers the enable timer and enable function. Enable is used to send data to M. NOC The gate provides the turn-on signal, and the Timer is used to specify the duration of the turn-on signal for Enable. M NOC The source is grounded, M NOC The drain of R3 is connected to one end of R3, and the other end of R3 is connected to one end of R4 and C. FOCV One end is connected and generates the current MPPT voltage V. MPPT The other end of R4 is connected to the input voltage V. IN C FOCV The other end is grounded; The ZCD sampling circuit is realized by a digital circuit, which is composed of a D flip-flop, the input end of the D flip-flop is connected with the voltage V SW of the SW node, the clock end is connected with the switch control signal Φ2, and the output end generates the zero-crossing signal ZCD_D. The logic control circuit includes a 6-bit arithmetic logic unit (ALU), a comparator, and two D flip-flops D1 and D2, wherein the non-inverting input of the comparator is connected to the input voltage V. IN The inverting input of the comparator is connected to the MPPT voltage. The ALU receives the comparator output comparison signal CMP_D, the zero-crossing signal, and the given clock signal CLK3. It controls the output of switch control signals Φ1 and Φ2 through internal logic. D1 is connected to the ALU and serves as a register for the switch control signal Φ1. Its clock input is connected to the given clock signal CLK1. CLK1 is used to control the input and output of D1 to Φ1. D2 is connected to the ALU and serves as a register for the switch control signal Φ2. Its clock input is connected to the given clock signal CLK2. CLK2 is used to control the input and output of D2 to Φ2.

2. The energy harvesting system of claim 1, wherein: The MPPT voltage V OCO is proportional to the open circuit voltage V OC measured at the last measurement, i.e. V OCO = k * V OC , k being a proportionality factor and fulfilling 1 + R2 / R1 = 1 / k.

3. The energy harvesting system of claim 1, wherein: The SW node is at the inductor current I L After zero crossing, the D flip-flop output ZCD_D is 0; the inductor current I L When not zero crossing, the D flip-flop output ZCD_D is 1, I L is the current flowing through the inductor L.

4. The energy-harvesting system of claim 1, wherein: the clock signal CLK3 is used for controlling the logic operation inside the ALU; due to the different working periods of the MPPT circuit and the ZCD sampling circuit, the ALU processes the output results of the MPPT circuit and the D flip-flop D1 when the high level of CLK3 is achieved, and the ALU processes the output results of the ZCD sampling circuit and the D flip-flop D1 when the low level of CLK3 is achieved, so that the multiplexing of the ALU is realized.

5. The energy-harvesting system of claim 1, wherein: The high level duration of the clock signals CLK2 and CLK3 is 0.5 mu s, the periods of CLK2 and CLK3 are 1 mu s and 8 mu s respectively, and the clock signal CLK1 is the result after the CLK3 is delayed by 100 ns.

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