Power generation system for self activation

A power generation system in an embodiment includes a power generator, a rectifying and smoothing circuit, a converter, a voltage measurement unit, and a switch. The power generator outputs AC power. The rectifying and smoothing circuit converts the AC power to DC power and smooths the DC power. The voltage measurement unit measures an average voltage of the AC power or a voltage of the smoothed DC power. The converter transforms the smoothed DC power. The switch is disposed between the rectifying and smoothing circuit and the converter, and becomes an ON state when the measured voltage becomes a reference voltage or higher.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2017-054574, filed on Mar. 21, 2017; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein generally relate to a power generation system.

BACKGROUND

A vibration power generator generates power utilizing environmental vibration (for example, vibration of vehicles and trains, or vibration of rain pelting on the ground). The power generated by the vibration power generator is expected as an alternative to the power supply (battery or the like) for use in a sensor or the like.

However, appropriate activation of a system including the vibration power generator is not always easy.

DETAILED DESCRIPTION

A power generation system in this embodiment includes a power generator, a rectifying and smoothing circuit, a converter, a voltage measurement unit, and a switch. The power generator outputs AC power. The rectifying and smoothing circuit converts the AC power to DC power and smooths the DC power. The voltage measurement unit measures an average voltage of the AC power or a voltage of the smoothed DC power. The converter transforms the smoothed DC power. The switch is disposed between the rectifying and smoothing circuit and the converter, and becomes an ON state when the measured voltage becomes a reference voltage or higher.

Hereinafter, a vibration power generation system in an embodiment will be explained referring to the drawings. Components with the same appended reference signs indicate the same components. Note that the drawings are schematic or conceptual.

A first embodiment will be explained.FIG. 1is a functional block diagram of a vibration power generation system1in a first embodiment.

The vibration power generation system1includes a vibration power generator10, a rectifying and smoothing circuit20, a converter30, a voltage measurement unit40, a reference output51, a comparator60, and a switch70.

FIG. 2is a cross-sectional view illustrating an example of the vibration power generator10. The vibration power generator10converts energy of vibration (mechanical energy) to AC power and outputs it. The vibration power generator10includes a case11, a vibrator12, a coil13, a coil fixing member14, an elastic member15.

The vibrator12is fixed to the elastic member15and suspended in the case11. The vibrator12has magnets12ato12cand yokes12fto12h.

The yoke12fis in an almost hollow columnar shape and surrounds the magnets12ato12cand the yokes12g,12h. An upper middle portion of the yoke12fis connected to the elastic member15.

The magnet12a, the yoke12g, the magnet12b, and the yoke12hare disposed in sequence along a center axis of the yoke12fon an inner upper surface of the yoke12f.

Each of the magnet12aand the magnet12bhas an N pole on the yoke12gside. As a result of this, magnetic fluxes repelling each other are generated from the magnets12a,12b.

The magnet12cis, for example, in a cylindrical shape, and is disposed on an inner side surface of the yoke12fwith a space interposed with respect to the outside of the coil13. The magnet12chas an S pole facing the coil13and an N pole in contact with the inner side surface of the yoke12f.

The coil13is in a ring shape, and is disposed on the outside of the magnets12a,and12band on the inside of the magnet12c. The coil13is wound in a circumferential direction, and its center axis is coincident with the center axis of the vibrator12(the case11).

The coil fixing member14fixes the coil13in the vibrator12. The coil fixing member14has a columnar coil support14afixed to a bottom surface of the case11. The coil fixing member14is fixed to the case11by the coil support14abut not fixed to the vibrator12(the magnets12ato12cand the yokes12g,12h).

The elastic member15is in a disk shape, and has a side surface fixed to the inner side surface of the case11and a lower surface partially connected to the vibrator12.

When external vibration is applied to the vibration power generator10, the coil13vibrates integrally with the case11. The vibrator12vibrates with a predetermined frequency with respect to the coil13according to the elastic force of the elastic member15. As a result of this, the vibrator12performs relative motion in the axial direction with respect to the coil13. Temporal change of the magnetic fluxes interlinking the coil13generates electromotive force.

The external vibration (mechanical energy) applied to the vibration power generator10is converted to AC power as described above. The vibration power generator10converts vibration (motion in the longitudinal direction in the drawing) directly to AC power here, but may convert vibration to AC power after converting vibration to rotational motion.

Note that the vibration power generator10may be replaced with generators in general (for converting mechanical energies in general to AC power) in this embodiment.

The rectifying and smoothing circuit20converts the AC power outputted from the vibration power generator10to smoothed DC power. The rectifying and smoothing circuit20has a rectifier circuit21and a smoothing circuit22.

The rectifier circuit21converts the AC power outputted from the vibration power generator10to DC power (typically, pulsating current). The rectifier circuit21can be composed of one or a plurality of diodes. For example, a full-wave rectifier in which four diodes are bridge-connected can be used as the rectifier circuit21.

The smoothing circuit22smooths the DC power (pulsating current) outputted from the rectifier circuit21. The smoothing circuit22can be composed of one or a plurality of capacitors, or a combination of a capacitor and a coil. The smoothing circuit22temporarily stores current (pulsating current) as electric charges, and discharges the electric charges to thereby smooth the voltage. In short, the smoothing circuit22is a kind of a power storage circuit that stores power.

The voltage measurement unit40, the reference output51, the comparator60, the switch70, and the converter30operate by the smoothed voltage outputted from the rectifying and smoothing circuit20. Therefore, the vibration power generation system1does not need battery or the like. This point also applies to other embodiments.

The converter30is, for example, a DC-DC converter, and transforms the DC power smoothed by the smoothing circuit22into a desired voltage. For example, the converter30converts the DC power to AC and transforms the AC power by a transformer or the like, and then returns the AC power to DC. The power outputted from the converter30(the vibration power generation system1) is supplied to an appropriate apparatus such as a sensor.

The voltage measurement unit40measures and outputs an average value (average voltage Va) of the output voltage outputted from the vibration power generator10. The average value is, as an example, a root mean square (RMS, effective value) of the voltage. The voltage measurement unit40may measure an envelope or the like in place of the average value of the output voltage. The voltage measurement unit40may output the voltage itself (hardware output), or may output a signal indicating the voltage value (software output).

The voltage measurement unit40has a voltage detector41and an averaging filter42.

The voltage detector41detects the AC voltage outputted from the vibration power generator10. More specifically, the voltage detector41outputs the voltage itself of the AC power outputted from the vibration power generator10or a signal indicating its voltage value.

The averaging filter42averages the AC voltage outputted from the voltage detector41to find the average value (average voltage Va). This averaging may be realized by either hardware or software.

The reference output51sets (stores) and outputs a reference voltage Vr. The reference output51may output either the voltage itself or a signal indicating its voltage value similarly to the voltage measurement unit40. As will be explained later, the reference voltage Vr is, for example, an average value of the output voltage corresponding to the time when the vibration power generator10is at die maximum output (when a load connected thereto is at an appropriate impedance).

The comparator60compares the average voltage Va measured by the voltage measurement unit40and the reference voltage Vr of the reference output51, and outputs an output signal when the average voltage Va becomes the reference voltage Vr or higher.

The switch70is disposed between the rectifying and smoothing circuit20and the converter30, and tarns ON/OFF the connection between them. At the activation time of the vibration power generation system1, the switch70is in an OFF state, and becomes an ON state upon reception of the output signal from the comparator60. More specifically, at the activation time of the vibration power generation system1, the smoothed DC voltage from the rectifying and smoothing circuit20is not applied to the converter30, but the smoothed DC voltage is applied to the converter30by output of the signal from the comparator60.

As illustrated inFIG. 3, the vibration power generator10receives environmental vibration and thereby generates power (Steps S1, S2), activating the vibration power generation system1.

For this activation, an activation switch or the like is not always needed. First, a switch (activation switch) is disposed between the vibration power generator10and the rectifying and smoothing circuit20and fee switch is turned ON, thereby enabling activation of the vibration power generation system1. On the other hand, even without such an activation switch, it can be considered that the vibration power generation system1is activated when vibration is applied to the vibration power generation system1. That is the time when the vibration power generation system1is installed under environmental vibration, or the time when vibration stops for a certain period after the installation and then vibration restarts.

When the vibration power generator10starts generating power, the impedance of the rectifying and smoothing circuit20increases (Step S3). Since the power is stored in the smoothing circuit (power storage circuit)22via the rectifier circuit21, the impedance of the smoothing circuit22increases. As a result of this, an impedance Z of the whole rectifying and smoothing circuit20also increases.

On the other hand, the output voltage from the vibration power generator10gradually rises from the activation time (Step S4). When the average value (average voltage Va) of the output voltage becomes the reference voltage Vr or higher, the switch70becomes the ON state (Steps S5, S6). As a result of this, the converter30is activated to start power supply to an external load such as a sensor (Steps S7, S8).

Note that, as will be explained later, the condition at Step S5“the average voltage Va becoming the reference voltage Vr or higher” is equivalent to “the impedance Z of the rectifying and smoothing circuit20becoming an appropriate impedance Zr or higher”.

When the average voltage Va becomes the reference voltage Vr or higher at the activation time of the vibration power generation system1as described above, the switch70is turned ON to supply power from the vibration power generator10to the converter30. This results in facilitation of appropriate activation of the vibration power generation system1as described in the following.

FIG. 4illustrates the connection state of the vibration power generator10, the rectifier circuit21, and the smoothing circuit22at the time when the switch70is OFF in the functional block diagram inFIG. 1. More specifically, the vibration power generator10, the rectifier circuit21, and the smoothing circuit (power storage circuit)22are connected in series.

In this case, temporal transitions of the output voltage (average voltage Va) from the vibration power generator10, the impedance Z (total of impedances of the rectifier circuit21and the smoothing circuit22) of the rectifying and smoothing circuit20connected to the vibration power generator10are as in graphs ofFIG. 5A,FIG. 5Brespectively. Further, as illustrated inFIG. 6, the impedance and the output voltage (average voltage) correspond in a one-to-one relationship.

Note that the impedance is obtained from the average voltage and average current as will be described later, and therefore can be considered as a kind of average value (RMS value).

The power generator including the vibration power generator10generally changes in output power depending on the impedance of a load. To maximize the output power, it is preferable to set the impedance of the load to an appropriate value (hereinafter, referred to as an “appropriate impedance Zr”).

However, when an electric circuit connected to the vibration power generator includes the smoothing circuit (power storage circuit), the impedance greatly changes while the smoothing circuit is charged. As a result, vibration power generator10cannot generate power efficiently.

FIG. 7is a graph made by overlapping the appropriate impedance Zr and the power from the vibration power generator10onFIG. 6. The average voltage corresponding to the appropriate impedance Zr is the reference voltage Vr, and the power from the vibration power generator10becomes maximum at this time. Therefore, the condition at Step S5in the flowchart inFIG. 3“the average voltage Va becoming the reference voltage Vr or higher” is equivalent to “the impedance Z of the rectifying and smoothing circuit20becoming the appropriate impedance Zr or higher”.

By turning on the switch70at the point in time when the impedance Z of the rectifying and smoothing circuit20reaches the appropriate impedance Zr, the converter30can be activated at a power generation maximum point. This enables efficient and stable supply from the point in time when starting the supply of power from the vibration power generation system1. If the switch70is not provided and the rectifying and smoothing circuit20and the converter30are directly connected, the operation of the converter30and the supply of power may become unstable or the power generation in the vibration power generator10may become inefficient.

Note that the reference voltage Vr can be experimentally obtained. Besides, when the appropriate impedance Zr is known, the reference voltage Vr can be calculated from the correspondence between the impedance Z and the average voltage Va.

A second embodiment will be explained.FIG. 8is a functional block diagram of a vibration power generation system1in the second embodiment.

As illustrated inFIG. 8, this embodiment is different from the first embodiment in that a voltage measurement unit40(a voltage detector41) measures (detects) the voltage outputted from a rectifying and smoothing circuit20. The other configuration is the same as that in the first embodiment.

The voltage detector41detects the smoothed voltage (DC) outputted from the rectifying and smoothing circuit20, thus eliminating the need for the averaging filter. This makes it possible to simplify the configuration and reduce the power consumption.

A third embodiment will be explained.FIG. 9is a functional block diagram of a vibration power generation system1in the third embodiment.

The third embodiment is different from the first embodiment in that an impedance storage (setting unit)52, a correspondence storage53, and a reference calculator54are further provided. The other configuration is the same as that in the first embodiment.

The impedance storage52sets (stores) impedance as a reference (hereinafter, reference impedance Zr). For example, the impedance is set by software. The reference impedance Zr to be set is preferably the appropriate impedance.

The correspondence storage53stores the correspondence between the impedance and the average voltage as illustrated inFIG. 7.

The correspondence between the impedance and the average voltage may be a data base or a statistical model or a mathematical model. Note that the statistical model or the mathematical model does not need to be precise but may be expressed in an average or approximate manner.

The reference calculator54calculates the reference voltage Vr from the reference impedance Zr set by the impedance storage52and the correspondence between the impedance and the average voltage supplied from the correspondence storage53.

According to this embodiment, the reference voltage Vr corresponding to the reference impedance Zr is uniquely calculated, and power can be taken out with high efficiency.

A fourth embodiment will be explained.FIG. 10is a functional block diagram of a vibration power generation system1in the fourth embodiment.FIG. 11is a graph illustrating an example of the correspondence among acceleration amplitude, impedance, and voltage.

As illustrated inFIG. 10, the fourth embodiment is different from the third embodiment in that a correspondence storage81, an accelerometer82, an amplitude calculator83, and a correspondence calculator84are provided in place of the correspondence storage53. The other configuration is the same as that in the third embodiment.

The correspondence storage81stores die correspondence among an acceleration amplitude A, a impedance Z, and an average voltage Va as illustrated inFIG. 11. Though the correspondence between the impedance Z and the average voltage Va when the acceleration amplitude A is defined is illustrated here, the correspondence among the acceleration amplitude A, the impedance Z, and the average voltage Va only needs to be illustrated in any form.

When the environmental vibration is stationary and periodic like a sine wave, the correspondence between the impedance Z and the average voltage Va changes according to the acceleration amplitude A of the environmental vibration.

This correspondence may be a data base or a statistical model or a mathematical model. Note that the statistical model or the mathematical model does not need to be precise but may be expressed in an average or approximate manner.

The accelerometer82is a measuring device that measures the acceleration of environmental vibration.

The amplitude calculator83calculates the amplitude (average amplitude) A of the measured acceleration.

The correspondence calculator84finds the correspondence between the impedance Z and the average voltage Va at the measured acceleration amplitude A on the basis of the acceleration amplitude A outputted from the amplitude calculator83and the correspondence stored in the correspondence storage81.

According to this embodiment, power can be taken out with high efficiency even when the correspondence between the impedance Z and the average voltage Va changes according to the amplitude A of the environmental vibration.

A fifth embodiment will be explained referring toFIG. 12,FIG. 13.FIG. 12is a functional block diagram of a vibration power generation system1in the fifth embodiment.FIG. 13is a graph illustrating the correspondence between a Q value of frequency characteristics of acceleration and appropriate impedance.

As illustrated inFIG. 12, this embodiment is different from the fourth embodiment in that a correspondence storage85, a frequency characteristics calculator86, a Q value calculator87, and an impedance calculator88are provided in place of the impedance storage52. The other configuration is the same as that in the fourth embodiment.

The correspondence storage85stores the correspondence between the Q value of the frequency characteristics of the acceleration and the appropriate impedance (reference impedance) Zr. In other words, the appropriate impedance of the vibration power generator10changes by the Q value of the frequency characteristics of the acceleration.

The correspondence between the Q value of the frequency characteristics of the acceleration and the appropriate impedance may be a data base or a statistical model or a mathematical model. Note that the statistical model or the mathematical model does not need to be precise but may be expressed in an average or approximate manner.

The frequency characteristics of die acceleration mean the frequency distribution of the acceleration amplitude. Generally, the environmental vibration is not stationary and periodic like a sine wave, but typically includes various frequency components. Therefore, the distribution of the frequency component of the acceleration amplitude affects the operation of the vibration power generator10.

The Q value of the frequency characteristics of the acceleration is a dimensionless number expressing a state of vibration and is defined as in following Expression (1)
Q=f0/ΔfExpression (1)

Here, f0is the frequency when the acceleration amplitude is at the peak, and Δf is the frequency amplitude in the acceleration amplitude decreased by 3 dB from the peak value.

The frequency characteristics calculator86outputs the frequency characteristics of the acceleration (frequency distribution of the acceleration amplitude). In other words, the correspondence between the frequency and the acceleration amplitude is found.

The Q value calculator87finds the frequency f0and the frequency amplitude Δf from the frequency characteristics of the acceleration, and further calculates the Q value of the frequency characteristics of the acceleration on the basis of Expression (1).

The impedance calculator88calculates the impedance at the Q value on the basis of the Q value of the acceleration frequency characteristics and the correspondence stored in the correspondence storage85.

According to this embodiment, power can be taken out with high efficiency even when the appropriate impedance changes according to the Q value of the acceleration frequency characteristics of environmental vibration.

A sixth embodiment will be explained referring toFIG. 14,FIG. 15.FIG. 14is a functional block diagram of a vibration power generation system1in the sixth embodiment.FIG. 15is a graph illustrating the correspondence among an acceleration amplitude A, a Q value of frequency characteristics of acceleration, an impedance Z, and an average voltage Va.

As illustrated inFIG. 14, this embodiment is different from the fifth embodiment in that a correspondence storage91and a correspondence calculator92are provided in place of the correspondence storage81and the correspondence calculator84and the Q value is inputted into the correspondence calculator92. The other configuration is the same as that in the fifth embodiment.

The correspondence storage91stores the correspondence among the acceleration amplitude A, the Q value of the acceleration frequency characteristics, the impedance Z, and the average voltage Va as illustrated inFIG. 15. Though the correspondence among the Q value of the acceleration frequency characteristics, the impedance Z, and the average voltage Va when the acceleration amplitude A is defined is three-dimensionally illustrated here, the correspondence among the acceleration amplitude A, the Q value of the acceleration frequency characteristics, the impedance Z, and the average voltage Va only needs to be illustrated in any form.

This correspondence may be a statistical model or a mathematical model. Note that the statistical model or the mathematical model does not need to be precise but may be expressed in an average or approximate manner.

As illustrated inFIG. 15, the correspondence calculator92derives the correspondence between the impedance and the voltage at the acceleration amplitude and the Q value, from the acceleration amplitude A, the Q value of the acceleration frequency characteristics, and the correspondence stored in the correspondence storage91.

According to this embodiment, power can be taken out with high efficiency even when the appropriate impedance Zr changes according to the acceleration amplitude A and the Q value.

A seventh embodiment will be explained referring toFIG. 16,FIG. 17.FIG. 16is a functional block diagram of a vibration power generation system1in the seventh embodiment.FIG. 17is a flowchart illustrating an operation procedure of the vibration power generation system1in the seventh embodiment.

As illustrated inFIG. 16, the vibration power generation system1includes a vibration power generator10, a rectifying and smoothing circuit20, a converter30, an impedance measurement unit93, a reference output94, a comparator60, and a switch70.

The impedance measurement unit93measures and outputs the impedance Z of the rectifying and smoothing circuit20.

The impedance measurement unit93has a voltage detector41, an averaging filter42, a cement detector43, an averaging filter44, and a divider45.

The current detector43detects AC current outputted from the vibration power generator10. More specifically, the current detector43outputs the current itself of the AC power outputted from the vibration power generator10or a signal indicating its current value.

The averaging filter44averages the AC current outputted from the current detector43to find its average value (average current Ia). This averaging may be realized by either hardware or software.

The divider45divides the average voltage and the average current outputted from the averaging filters42,44respectively to calculate the impedance Z.

Both of the voltage and the current outputted from the vibration power generator10are AC. When the AC voltage and the AC current are subjected to division, a section where division by 0 arises, causing a situation undesirable to calculate an average impedance. For this reason, the voltage and the current averaged by the averaging filters42,44are subjected to division.

The reference output94outputs a signal corresponding to the reference impedance Zr.

The comparator60outputs an output signal when the impedance Z becomes the reference impedance Zr.

The impedance measurement unit93in addition to the reference output51, the comparator60, the switch70, and the converter30are operated by the smoothed voltage outputted from the rectifying and smoothing circuit20.

Note that explanation of components in common to the other embodiments will be omitted.

As illustrated inFIG. 17, at the activation time of the vibration power generation system1, the vibration power generator10generates power upon reception of environmental vibration and the impedance Z of the rectifying and smoothing circuit20increases (Steps S1to S3). When the impedance Z becomes the reference impedance Zr or higher, the switch70is turned ON (Steps S51, S6). As a result of this, the converter30is activated to start power supply to an external load such as a sensor (Steps S7, S8).

In this embodiment, the impedance is directly measured, thereby eliminating the need for the step of calculating the reference voltage Vr.

An eighth embodiment will be explained.FIG. 18is a functional block diagram of a vibration power generation system1in the eighth embodiment.

This embodiment is different from the seventh embodiment in that the impedance is the one ahead the rectifying and smoothing circuit20. The other configuration is the same as that in the seventh embodiment.

In this case, the voltage detected by the voltage detector41is inputted as it is into the divider45, whereas the current detected by the current detector43is averaged by the averaging filter44and then inputted into the divider45. This is because the voltage detected by the voltage detector41is generally smoothed, whereas the current detected by the current detector43is still a pulsating current.

As has been described, the DC power of pulsating current is outputted from the rectifier circuit21. Both of the voltage and the current of the power outputted in this case are pulsating current. The smoothing circuit29stores electric charges until the voltage rises to a certain level, and thereby smooths the voltage of pulsating current (the voltage of the rectifying and smoothing circuit20is decided by the electric charges stored in the smoothing circuit29). On the other hand, the smoothing circuit29less smooths the current than the voltage.

A ninth embodiment will be explained.FIG. 19is a functional block diagram of a vibration power generation system1in the ninth embodiment.

The ninth embodiment is different from the seventh embodiment in that an accelerometer82, an amplitude calculator83, a correspondence storage95, and a reference calculator96are further provided. The other configuration is the same as that in the seventh embodiment.

The correspondence storage95stores the correspondence between an acceleration amplitude A and an appropriate impedance Zr.

The reference calculator96calculates die reference impedance Zr on the basis of the correspondence between the acceleration amplitude A and the appropriate impedance Zr from the correspondence storage53and the acceleration amplitude A from the amplitude calculator83.

The other configuration is the same as that in the fourth embodiment, and explanation thereof will be omitted.

According to this embodiment, power can be taken out with high efficiency even when the appropriate impedance Zr changes according to the acceleration amplitude A.