SELF-POWERED SYSTEM AND METHOD FOR POWER EXTRACTION AND MEASUREMENT OF ENERGY-GENERATOR UNITS

Abstract

A self-powered system and a method for power extraction and measurement of energy-generator units are disclosed. The system comprises an energy generator unit (10) providing an electrical current I.sub.FC and a voltage V.sub.FC; an instrumentation block (20) to measure the electrical current I.sub.FC; and a power management unit (30) connected to the energy generator unit (10) via a first input that collects the electrical current I.sub.FC, extracting an electrical power provided by the energy generator unit (10). The power management unit (30) also has a second input which is connected to a feedback element (40) connected to a voltage reference V.sub.REF, to the voltage V.sub.FC and to the instrumentation block (20). A variation of an equivalent input impedance of the power management unit (30) sets a given parameter of the energy generator unit (10) to a controlled given value and the instrumentation block (20) assists in the control of the parameter.

Claims

1. A self-powered system, comprising: an energy generator unit configured to provide an electrical current I.sub.FC and a voltage V.sub.FC; an instrumentation block electrically connected to said energy generator unit and configured to measure said electrical current I.sub.FC provided by said energy generator unit; a power management unit electrically connected to said energy generator unit via a first input to collect said electrical current I.sub.FC, and configured to extract an electrical power provided by the energy generator unit; a feedback element electrically connected to said power management unit via a second input of said power management unit, said feedback element further being electrically connected to a voltage reference V.sub.REF, to the voltage V.sub.FC provided by said energy generator unit and to an input of said instrumentation block, such that, simultaneously to the extraction of the electrical power by the power management unit, said power management unit, and said instrumentation block are cooperatively configured to set a given parameter of said energy generator unit to a controlled given value by varying an equivalent input impedance of said power management unit, said energy generation unit, said power management unit, said feedback element and the voltage reference V.sub.REF being collectively structured to define a closed loop controller system.

2. The system according to claim 1, wherein said given parameter set by said equivalent input impedance of said power management unit is a polarization voltage of said energy generator unit.

3. The system according to claim 1, wherein said energy generator unit comprises a fuel cell.

4. The system according to claim 1, wherein said instrumentation block comprises a current measurement module electrically connected to said energy generator unit to provide a differential potential V.sub.S proportional to said electrical current I.sub.FC, and an instrumentation amplifier, said instrumentation amplifier being connected to said current measurement module via a first input and to said energy generator unit via a second input, so that said instrumentation amplifier amplifies the differential potential V.sub.S and provides a voltage signal V.sub.SENSE proportional to the measured electrical current.

5. The system according to claim 4, wherein said current measurement module comprises a shunt resistor or a hall sensor.

6. The system according to claim 3, wherein said fuel cell is a glucose, ethanol, lactate or methanol fuel cell.

7. The system according to claim 1, wherein the power management unit comprises a DC-DC converter, and wherein said equivalent input impedance is set by varying a duty cycle of said DC-DC converter.

8. The system according to claim 1, wherein the power management unit comprises a DC-DC converter, and wherein said equivalent input impedance is set by a frequency modulation technique of said DC-DC converter.

9. The system according to claim 1, wherein said power management unit further comprises a maximum power point tracking (MPPT) component configured to adapt said equivalent input impedance to set an electrical voltage of said power management unit to said voltage reference V.sub.REF.

10. The system according to claim 1, wherein said instrumentation block, said power management unit and said feedback element are integrated in a silicon chip.

11. A method for power extraction and measurement of energy-generator units, comprising: providing an energy generator unit that delivers an electrical current I.sub.FC and a voltage V.sub.FC; providing an instrumentation block electrically connected to the energy generator unit, and using the instrumentation block to measure the electrical current I.sub.FC delivered by the energy generator unit; providing a power management unit electrically connected to the energy generator unit via a first input configured to collect the electrical current I.sub.FC, using the power management unit to extract an electrical power provided by the energy generator unit; providing a feedback element electrically connected to the power management unit via a second input of the power management unit, the feedback element being further connected to a voltage reference V.sub.REF, to the voltage V.sub.FC provided by the energy generator unit and to an input of the instrumentation block; and simultaneously to the power extraction, using the power management unit and the instrumentation block to set a given parameter of the energy unit to a controlled given value by varying an equivalent input impedance of the power management unit, the energy generation unit, the power management unit, the feedback element and the voltage reference V.sub.REF being collectively structured to define a closed loop controller system.

12. The method according to claim 11, wherein the given parameter is a polarization voltage of the energy generator unit, which is a fuel cell including a glucose, ethanol, lactate or methanol fuel cell.

13. The method according to claim 11, wherein the power management unit comprises a DC-DC converter, and wherein the equivalent input impedance is set by varying a duty cycle of the DC-DC converter or by a frequency modulation technique of the DC-DC converter.

14. The method according to claim 11, further comprising setting an electrical voltage of the power management unit to the voltage reference V.sub.REF by a maximum power point tracking (MPPT) component.

15. The system of claim 1, configured as a point-of care device.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0035] FIG. 1A and FIG. 1B schematically illustrate common potentiostat architectures used for fuel cell characterization according to the prior art.

[0036] FIG. 2 is a block diagram of a self-powered system, according to an embodiment of the present invention.

[0037] FIG. 3 is a block diagram of the closed-loop controller structure of the self-powered system of FIG. 2.

[0038] FIG. 4 is a schematic of a prototype implemented to show the performance of the proposed self-powered system.

[0039] FIG. 5 is a flow chart illustrating a method for power extraction and measurement of energy-generator units, according to an embodiment of the present invention.

[0040] FIG. 6 illustrates the measurement concentration and efficiency of a methanol fuel cell, according to an embodiment of the present invention.

[0041] FIG. 7 is a block diagram of a self-powered system, according to an embodiment of the present invention.

[0042] FIG. 8 illustrates the voltage-current characteristic of the energy generator unit of FIG. 7 for different temperature gradients.

[0043] FIG. 9 illustrates the gradient temperature to current transfer function of the energy generator unit of FIG. 7 for a polarization voltage of 0.15 V.

DESCRIPTION OF EMBODIMENTS

[0044] Provided herein are a self-powered system for energy-generator units diagnostic with sensitive-output-characteristics, and a related method for power extraction and concentration measurement of energy-generator units.

[0045] FIG. 2 illustrates a self-powered system in accordance with an embodiment of the present invention. The system of FIG. 2 includes an energy generator unit 10 that delivers/provides an electrical current I.sub.FC and a voltage V.sub.FC, an instrumentation block electrically connected to the energy generator unit 10 to measure the electrical current I.sub.FC, a power management unit 30, or PMU from now on, and a feedback element 40, in this particular case implemented as a feedback amplifier.

[0046] The PMU 30 is electrically connected to the energy generator unit 10 via a first input and to the feedback element 40 via a second input. The feedback element 40 is electrically connected to a voltage reference V.sub.REF provided by element 50, in this particular embodiment a Zener diode, to an input of the instrumentation block 20 and to the voltage V.sub.FC provided by the energy generator unit 10.

[0047] In the proposed self-powered system, the PMU 30 is the responsible of setting a parameter of the energy generator unit 10 to a controlled given value and the instrumentation block 20 is the responsible of controlling (or assists in the control of) the parameter. The PMU 30 varies its equivalent input impedance in order to lead the parameter to the desired value.

[0048] In an embodiment, the equivalent input impedance is set by varying the duty cycle of a DC-DC converter (not shown) of the PMU 30. The duty cycle acts as a control signal setting the input impedance of the PMU 30 of a closed-loop controller system formed by the energy generator unit 10, the PMU 30, the feedback element 40 and the voltage reference V.sub.REF. Block diagram of the closed-loop controller system is shown in FIG. 3.

[0049] Moreover, the PMU 30 can also include a maximum power point tracking (MPPT) component that adapts the equivalent input impedance to set the electrical voltage of the PMU 30 to the voltage reference V.sub.REF.

[0050] The criteria to select the voltage level of the voltage reference V.sub.REF is application-dependent and a trade-off between the energy generator unit 10 performance as a sensor and as a power source must be considered.

[0051] In a particular embodiment, the energy generator unit 10 is a fuel cell such as a glucose, ethanol, lactate or methanol fuel cell. It should be noted that other fuel cells can be also used. In the specific case of using a fuel cell, the PMU 30 varies its equivalent input impedance in order to lead the polarization voltage of the fuel cell to the desired level. Furthermore, for a fuel cell with a better performance as a power source than as a sensor, the polarization voltage will be set closer to V.sub.SENSOR (i.e. the polarization voltage) in order to maximize the specifications related to the measurement (sensitivity, repeatability or linearity, among others) in detriment of lower power extraction from the fuel cell. On the other hand, when better performance as a sensor than as a power source is required, the polarization voltage will be set closer to V.sub.P.sub.MAX in order to maximize the power extracted from the fuel cell.

[0052] The instrumentation block 20 can comprise a current measurement module 21 and an instrumentation amplifier 22. The current measurement module 21 is placed in series in the current path between the energy generator unit 10 and the PMU 30. Multiple circuits, sensors and techniques can be used to measure the electrical current I.sub.FC (from current measurements modules based in a Hall effect sensor, when high current levels are measured (preferably mA to several A), to current measurement modules based in a shunt, when ultra-low current levels are measured, (preferably from pA to μA), among other solutions to extract a current measurement such as current mirrors, transformers, etc. Again, the measurement technique must be selected as a function of a trade-off between the electrical current levels to be measured and the power available from the energy generator unit 10.

[0053] The proposed system provides two major benefits in front of other implementations: 1) the measurement is performed simultaneously with the power extraction, and 2) the energy is extracted with maximum efficiency from the energy generator unit point of view. Common chronoamperometries can take up to several minutes. During these periods, in the common approach of timemultiplexing, PMU 30 remains disconnected and no power is extracted from the energy generator unit 10. This is translated to a previous longer power-extraction times to extract enough energy to perform the measurement, or, directly, to the infeasibility of the measurement. In both cases, not all power generated by the energy generator unit 10 is extracted due to the PMU 30 disconnection during measurement periods. The first benefit solves this by extracting power and measuring simultaneously. The second benefit is achieved when the cited parameter of the energy generator unit 10 is set to a maximum value. Thus, maximum power available from the energy generator unit 10 is achieved allowing longer operation times and/or the possibility of adding more complex (and then with higher power consumption) electronics that allows a better measurement performance or added functionalities (wireless transmission or graphic user interface, among others). In this case, a power extraction level is achieved with the only limitation coming from the energy generator unit 10 performance itself.

[0054] A prototype using current available Commercial Off-The-Shelf (COTS) discrete components has been implemented to show the performance of the proposed self-powered system. The ubiquitous characteristic of the proposed system has been validated with different state-of-the-art fuel cells. A detail explanation is described as follows.

[0055] State-of-the-art of fuel cells present ranges of the volume from few μL to L. Among some of them, in the case of enzymatic fuel cells, volumes are in the range of μL to mL. Some cases were emulated using a Source Meter Unit (SMU). The SMU permits to emulate real polarization curves extracted from literature. Ethanol and lactate fuel cells were emulated. The fuel cells were also validated with a non-emulated methanol-based fuel cell. A commercial Direct Methanol Fuel Cell (DMFC) was chosen. The DFMC can operate with methanol solutions with concentrations up to 1 M.

[0056] The system has been implemented on a double-sided Printed Circuit Board (PCB). FIG. 4 shows a schematic thereof. As a PMU 30, a BQ25504 boost converter was used. In terms of the energy generator unit nature and configuration, input voltage can vary from low voltage levels of few μV to hundreds mV. The BQ25504 provides a regulated output voltage, with the MPPT enabled, from 1.8V up to 3.6V from a lower input voltage. Below 1.8V, the MPPT functionality remains disabled. The regulated output voltage is indicated as V.sub.DD and is used to power the front-end and back-end modules, and the user interface. The converter also provides a Power Good (PGOOD) signal that is configured to go high when V.sub.DD reaches a voltage level of 3.0V and to go low when it decreases under 2.5V.

[0057] The MPPT functionality is used to control the input voltage of the PMU 30 in node V.sub.OP. It adapts its equivalent input impedance to set the input voltage equal to the reference voltage V.sub.REF. The reference voltage V.sub.REF is set, in this case, provided through a high impedance voltage divider 50, to the voltage level where maximum power is extracted from the fuel cell to be used. These optimal voltage levels are 500 mV 225 mV and 200 mV for the fuel cells based in ethanol, lactate and methanol, respectively.

[0058] It should be observed that this BQ25504-based implementation slightly differs from the block diagram of FIG. 2. While the purposed solution controls the voltage level at the node indicated as V.sub.FC, the BQ25504 has a non-accessible integrated control amplifier that controls the voltage level at the node V.sub.OP in FIG. 4. Even so, in a full-custom integrated approximation, voltage level at the node V.sub.FC should be controlled by the feedback element 40.

[0059] The electrical current delivered/provided by the fuel cell was measured through a shunt resistor and an instrumentation amplifier 22 that provides a signal, indicated as V.sub.SENSE, proportional to the measured current. The instrumentation amplifier in this case consisted of a dual operational amplifier. The shunt resistor and instrumentation amplifier 22 gain values were set to 15 and 28.8 VV.sup.−1, 15 and 22.3 VV.sup.−1, and 0.1 and 77.9 VV.sup.−1 for the fuel cells based in ethanol, lactate and methanol, respectively.

[0060] For illustration purposes, a back-end module based in a microcontroller module and a user interface based in a LCD display were implemented for the case of a fuel cell based in methanol.

[0061] Electrochemical experiments for methanol fuel cell characterization were carried out with the SMU and validated with non-emulated DMFC. Electrochemical experiments were carried out for a concentration range from 0.3 to 0.7 M with concentration steps of 0.1 M. For a given concentration, OCV was stable and above the expected OCV of 500 mV, polarization curve was extracted between OCV and 0 V at a scan rate of 1 mV s.sup.−1.

[0062] The system has been fully characterized in terms of power consumption, transfer function, power efficiency from fuel cell point of view and start-up time. The power consumption was measured with the SMU. The transfer functions for the different fuel cells, emulated and implemented, have been extracted by measuring V.sub.SENSE for different fuel concentrations once steady-state operation is reached. The analog signal was captured with an oscilloscope. The power efficiency was measured by monitoring the current, using SMU facilities. Start-up characterization was performed by capturing V.sub.FC, V.sub.DD, V.sub.REF, V.sub.SENSE and V.sub.PGOOD during the system's start-up transient with two oscilloscopes along with the SMU in common triggered configuration.

[0063] The solution exhibited a minimum efficiency and maximum start-up time for the ethanol, lactate and methanol-based fuel cells of 95% and 9 s, 90% and 12 s, and 85% and under 1 s, respectively.

[0064] The present invention also relates to a method for simultaneous power extraction and concentration measurement of energy-generator units.

[0065] FIG. 5 shows an embodiment of the method. The method starts by providing an electrical current I.sub.FC and a voltage V.sub.FC by an energy generator unit (step 501). When an instrumentation block is electrically connected to the energy generator unit, the instrumentation block measures the electrical current I.sub.FC (step 502). The PMU then extracts an electrical power provided by the energy generator unit (step 503) and simultaneously sets a given parameter of the energy generator unit to a controlled value (step 504) by varying its equivalent input impedance. The instrumentation block assists in the control of the parameter.

[0066] In a specific embodiment, the given parameter is the polarization voltage of a fuel cell.

[0067] With reference to FIG. 6, therein it is illustrated the measurement concentration and efficiency of a methanol fuel cell, according to a particular embodiment of the present invention. The transfer function has been extracted by measuring V.sub.SENSE in terms of the concentration for the emulated and experimental fuel cell. There is a direct relationship between the lecture and the concentration of the sample. In terms of efficiency, the extracted energy is kept very high while the measurement takes place. The small deviation between these data validates the methodology for the emulated fuel cells.

[0068] Although specific embodiments have been detailed using a fuel cell as energy generator unit 10, the teaching of the present invention can be applied to other energy generator units such as galvanic cells, electrical energy transducers, thermoelectric generators (TEG), or electrical batteries, among others.

[0069] In particular, FIG. 7 illustrates an embodiment of the proposed self-powered system using a TEG as energy generator unit 10. The voltage-current characteristic of a commercial off-the-shelf thermoelectric generator for different temperature gradients is shown in FIG. 8. Varying the equivalent input impedance of the PMU 30, the operating point of the TEG is controlled to a desired state by means of the thermoelectric generator's output voltage. Once fixed, measuring the current outputted by the TEG, a parameter related to the TEG can be measured. In this application-specific case, the temperature gradient across the thermoelectric generator can be monitored, as depicted in FIG. 9.

[0070] The foregoing describes embodiments of the present invention and modifications, obvious to those skilled in the art can be made thereto, without departing from the scope of the present invention.