JP2007005371A - Thermoelectric generator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoelectric generator capable of making output of the thermoelectric generator follow the maximum power in accordance with an actual voltage current characteristic when power is generated. <P>SOLUTION: The actual voltage current characteristic V=Vo-(R+αβ)I into which a temperature change due to a Peltier effect of a thermal generation module is taken is estimated when the thermal generator generates power, and a target current value Ip=Vo/2(R+αβ) corresponding to the maximum power in the actual voltage current characteristic is obtained. A correction voltage value for changing the current value of the thermal generator module so the current value follows the maximum current using the target current value Ip as a center of searching is obtained as V-V1. Accordingly, the current value is changed with the corrected voltage value, thereby controlling the output of the thermal generator so that it may follow the maximum power in accordance with the actual voltage current characteristic in operation. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a thermoelectric power generation apparatus that directly converts thermal energy into electrical energy by a thermoelectric power generation module, and more particularly to a thermoelectric power generation apparatus that is output-controlled so as to track maximum power.

  The thermoelectric power generation module includes a plurality of n-type thermoelectric power generation elements and p-type thermoelectric power generation elements that generate a thermoelectromotive force according to a temperature difference by the Seebeck effect between a high-temperature side heat transfer member and a low-temperature side heat transfer member. It has an installed structure and can directly convert thermal energy into electrical energy. And a thermoelectric generator is comprised by making a high heat source contact the high temperature side heat transfer member of such a thermoelectric power generation module, and making a low temperature side heat transfer member contact a cooling source.

  In this type of thermoelectric generator, as in the solar power generator described in Patent Document 1, for example, the output is controlled to track the maximum power by conventionally known MPPT (Muximum Power Point Tracker) control.

Here, in the MPPT control of the thermoelectric generator, the output current changes at a high frequency of several Hz or more around the target current value corresponding to the maximum power (power peak) according to the voltage-current characteristics of the output of the thermoelectric generator. The output current increase / decrease is determined while maintaining the change direction of the output current when the output power increases, and by reversing the change direction of the output current when the output power decreases, the average current The value is controlled to approach the target current value.
Japanese Patent Laid-Open No. 08-179840 (paragraph numbers 3 and 4)

  By the way, in the above-described thermoelectric power generation device, when the output current value increases from the open circuit voltage value of zero output current value due to the power generation action, heat absorption due to the Peltier effect of the thermoelectric power generation module, the heat generation phenomenon causes the high temperature of the thermoelectric power generation element. The temperature on the side decreases and the temperature on the low temperature side increases. For this reason, the temperature gradient in the thermoelectric power generation element becomes smaller, the electromotive force of each thermoelectric power generation element decreases, and the output voltage of the thermoelectric power generation apparatus deviates from the initial voltage-current characteristics.

  Therefore, in the MPPT control of the conventional thermoelectric generator, the target current value cannot be accurately determined in accordance with the actual voltage-current characteristics accompanying the operation of the thermoelectric generator, and as a result, the output of the thermoelectric generator is maximized. There is a problem that it is difficult to reliably track electric power, and this problem cannot be ignored when the power generation performance of the thermoelectric power generator is improved.

  Then, this invention makes it a subject to provide the thermoelectric generator which can track the output of a thermoelectric generator to maximum electric power according to the actual voltage-current characteristic at the time of electric power generation.

  A thermoelectric power generation device according to the present invention is a thermoelectric power generation device that is output-controlled so as to track the maximum power based on the voltage-current characteristics of the thermoelectric power generation module. Means for estimating the actual voltage-current characteristics in consideration, means for obtaining the target current value corresponding to the actual maximum power from the estimated voltage-current characteristics, and tracking the maximum power with the obtained target current value as the search center And a means for obtaining a correction voltage value for changing the current value.

  In the thermoelectric generator according to the present invention, an actual voltage-current characteristic is estimated in consideration of a change in temperature gradient due to the Peltier effect of the thermoelectric generator module at the time of power generation, and corresponds to the actual maximum power from the estimated voltage-current characteristic. A target current value is obtained. Then, a correction voltage value for changing the current value so as to track the maximum power with the obtained target current value as a search center is obtained. Therefore, by changing the current value with this correction voltage value, the output of the thermoelectric power generator is controlled to track the maximum power in accordance with the actual voltage-current characteristics during power generation.

  In the thermoelectric generator according to the present invention, an actual voltage-current characteristic is estimated in consideration of a change in temperature gradient due to the Peltier effect of the thermoelectric generator module at the time of power generation, and corresponds to the actual maximum power from the estimated voltage-current characteristic. A target current value is obtained. Then, a correction voltage value for changing the current value so as to track the maximum power with the obtained target current value as a search center is obtained. Therefore, according to the present invention, by changing the current value with the correction voltage value, the output of the thermoelectric generator can be tracked to the maximum power in accordance with the actual voltage-current characteristics during power generation.

  Embodiments of a thermoelectric generator according to the present invention will be described below with reference to the drawings. In the drawings to be referred to, FIG. 1 is a perspective view showing a schematic structure of a thermoelectric power generation module constituting a thermoelectric power generation device according to an embodiment, and FIG. 2 is a change in temperature gradient accompanying a power generation action of the thermoelectric power generation module shown in FIG. FIG. 3 is a block configuration diagram of an output control system of a thermoelectric power generation apparatus including the thermoelectric power generation module shown in FIG.

  A thermoelectric generator according to an embodiment includes a thermoelectric generator module 1 having a structure as shown in FIG. This thermoelectric power generation module 1 includes a heat receiving substrate 1A made of insulating ceramics in which an n-type thermoelectric power generation element N and a p-type thermoelectric power generation element P that generate thermoelectromotive force according to a temperature difference by the Seebeck effect are heat transfer members on a high temperature side. And a plurality of insulating ceramics heat dissipation substrates 1B, which are heat transfer members on the low temperature side, and these n-type thermoelectric generation elements N and p-type thermoelectric generation elements P are alternately arranged via electrode plates 1C. It has a basic structure connected in series.

  As shown in FIG. 2, the thermoelectric power generation module 1 having such a structure is connected in series by the heat receiving substrate 1 </ b> A contacting the appropriate high heat source 2 and the heat radiating substrate 1 </ b> B contacting the appropriate cooling source 3. Each n-type thermoelectric generator N and p-type thermoelectric generator P (see FIG. 1) generates thermoelectromotive force to generate electricity.

  Here, since each n-type thermoelectric power generation element N and p-type thermoelectric power generation element P has a Peltier effect, when the output current increases in accordance with the power generation action of the thermoelectric power generation module 1, each n-type thermoelectric power generation element P is affected by heat absorption and heat generation. The temperature on the high temperature side of the thermoelectric power generation element N and the p-type thermoelectric power generation element P decreases, and the temperature on the low temperature side increases. That is, the temperature gradient in the thermoelectric generator module 1 changes from the initial temperature gradient shown by the solid line in FIG. 2 to the temperature gradient shown by the dotted line, and the temperature gradient of each n-type thermoelectric generator N and p-type thermoelectric generator P increases. The temperature difference between the temperature Th and the temperature Tc on the low temperature side is gradually reduced, and the electromotive force of each n-type thermoelectric generator N and p-type thermoelectric generator P is lowered.

  Therefore, in order to take out the maximum power (power peak) from the power generation output of the thermoelectric power generation module 1 accompanied by such a change in temperature gradient, the thermoelectric power generation apparatus according to one embodiment includes an arithmetic control unit 4 as shown in FIG. A current control unit 5 and a voltage conversion unit 6 are provided.

  The arithmetic control unit 4 and the current control unit 5 are configured by using microcomputer hardware and software, and an input / output interface I / O, an A / D converter, a ROM (Read Only Memory) storing programs and data. ), A RAM (Random Access Memory) that temporarily stores input data and the like, a CPU (Central Processing Unit) that executes a program, and the like as hardware.

  The arithmetic control unit 4 and the current control unit 5 execute conventionally well-known MPPT (Muximum Power Point Tracker) control based on the voltage signal input from the thermoelectric power generation module 1. At this time, as will be described later, Control is performed so that the output of the thermoelectric power generation module 1 is tracked to the maximum power (power peak) in accordance with the actual voltage-current characteristics in consideration of changes in temperature gradient due to the Peltier effect during power generation of the module 1.

  The current control unit 5 includes a chopper circuit, and a pulsating voltage having a maximum voltage value V (M) and a minimum voltage value V (m) as shown in FIG. , That is, the pulsating current having the maximum current value I (M) and the minimum current value I (m) that pulsate around the average current value I (mean), is output to the voltage converter 6.

  The voltage conversion unit 6 includes a DC-DC converter, converts a DC voltage corresponding to the average current value I (mean) of the pulsating current input from the current control unit 5 into a required voltage of the load, and outputs it.

  Here, the arithmetic control unit 4 corresponds to a first means for estimating an actual voltage-current characteristic in consideration of a change in temperature gradient accompanying the power generation operation of the thermoelectric power generation module 1 and the actual maximum power of the thermoelectric power generation module 1. The second means for obtaining the target current value to be performed and the third means for obtaining the correction voltage value for changing the current value so as to track the maximum power with the obtained target current value as the search center are configured as software. Yes.

  FIG. 5 shows the voltage-current characteristics of the thermoelectric power generation module 1. In the figure, the voltage-current characteristics indicated by the two-dot chain line are ideals ignoring changes in the temperature gradient due to the Peltier effect associated with the power generation operation of the thermoelectric power generation module 1. It is a characteristic. This ideal characteristic is that the initial value of the temperature difference T between the high temperature side temperature Th and the low temperature side temperature Tc of the n-type thermoelectric power generation element N and the p-type thermoelectric power generation element P is To, and the thermoelectric power generation module corresponds to the temperature difference To. When the open circuit voltage at zero current of 1 is Vo, the internal resistance by the n-type thermoelectric generator N and the p-type thermoelectric generator P is R, and the output current value of the thermoelectric generator module 1 is I, V = Vo-RI It is expressed by a formula.

  On the other hand, the voltage-current characteristic indicated by the solid line in FIG. 5 is an actual static characteristic that takes into account a change in temperature gradient due to the Peltier effect associated with the power generation operation of the thermoelectric power generation module 1. The first means is estimated by the following procedure. First, Voc is the open circuit voltage at zero current of the thermoelectric generator module 1 corresponding to the temperature difference T described above, and α is an invariant constant determined by the material and design of the n-type thermoelectric generator N and p-type thermoelectric generator P. Since the open circuit voltage Voc is proportional to the temperature difference T with a proportional constant α, the equation (1) of Voc = αT is established.

  The temperature difference T decreases in proportion to the output current I of the thermoelectric power generation module 1 from the initial value To due to the Peltier effect of the n-type thermoelectric power generation element N and the p-type thermoelectric power generation element. When an constant constant determined by the material and design of the element N, the p-type thermoelectric power generation element P, the heat receiving substrate 1A, and the heat dissipation substrate 1B is β, the equation (2) of T = To−βI is established. Then, the equation (3) of V = Voc-RI is established in the same manner as the ideal characteristic equation V = Vo-RI described above.

  Here, when formula (1) is substituted into Voc of formula (3) and formula (2) is substituted into T of the formula and rearranged, V = αTo− (R + αβ) I is obtained. On the other hand, the open circuit voltage Vo corresponding to the initial value To of the temperature difference T described above is expressed by Vo = αTo as in the equation (1). Therefore, by replacing αTo with Vo, equation (4) of V = Vo− (R + αβ) I is obtained. That is, the first means of the arithmetic control unit 4 uses the actual static characteristic considering the change of the temperature gradient due to the Peltier effect accompanying the power generation operation of the thermoelectric power generation module 1 as the equation (4) of V = Vo− (R + αβ) I. presume.

  Incidentally, when the current control unit 5 outputs a pulsating current having a high frequency of several Hz or more as shown in FIG. 4 in accordance with the MPPT control by the arithmetic control unit 4 and the current control unit 5 shown in FIG. Since the change in the temperature gradient in the power generation module 1 does not follow the current fluctuation, the actual static characteristics of the thermoelectric power generation module 1 are apparently dynamic characteristics indicated by dotted lines in FIG. This dynamic characteristic is obtained by ignoring the αβ term in the equation (4) of V = Vo− (R + αβ) I, and the equation of V = Vc−RI parallel to the ideal characteristic shown by the two-dot chain line in FIG. It is represented by (5). In this equation (5), Vc is a constant that changes according to the search center value of the target current value by MPPT control.

  However, the current value Ic corresponding to the maximum power (power peak) in the apparent dynamic characteristic indicated by the dotted line in FIG. 5 is the maximum power (power peak) in the actual static characteristic of the thermoelectric power generation module 1 indicated by the solid line in FIG. Is different from the target current value Ip corresponding to. Therefore, the second means of the calculation control unit 4 obtains this target current value Ip. That is, the second means sets V = 0 in the equation (4) of V = Vo− (R + αβ) I estimated by the first means as the actual static characteristic of the thermoelectric power generation module 1 shown by a solid line in FIG. 1/2 of the satisfactory current value I is obtained as the target current value Ip. This target current value Ip is expressed by Expression (6) where Ip = Vo / 2 (R + αβ).

  Next, a correction voltage value for changing the current value of the thermoelectric power generation module 1 so as to track the maximum power (power peak) with the target current value Ip obtained by the second means of the arithmetic control unit 4 as the search center is obtained. The third means obtains by the following procedure. Here, the voltage-current characteristic indicated by the broken line in FIG. 5 is a dynamic characteristic obtained by correcting and correcting the apparent dynamic characteristic voltage indicated by the dotted line by V1, and the current value Io at V = 0 is the actual value indicated by the solid line in FIG. The current value Ip ′ corresponding to the maximum power (power peak) matches the aforementioned target current value Ip. Therefore, if the voltage correction amount V1 is known, the target voltage can be obtained by using the correction voltage value obtained by correcting the apparent dynamic characteristic shown by the dotted line and the equation (5) of V = Vc−RI in FIG. 5 by the voltage correction amount V1. The current value of the thermoelectric power generation module 1 can be changed so as to track the maximum power (power peak) with the current value Ip = Ip ′ as the search center.

  Therefore, the third means of the arithmetic control unit 4 obtains a corrected voltage value obtained by correcting the apparent dynamic characteristic represented by the dotted line and the equation (5) of V = Vc−RI in FIG. 5 by the voltage correction amount V1. First, in the apparent dynamic characteristic expressed by the equation (5) of V = Vc−RI, the target current value Ip expressed by the equation (6) of Ip = Vo / 2 (R + αβ) is used as the search center. A constant Vc is obtained, and a current value Ip ′ corresponding to the maximum power (power peak) indicated by a broken line in FIG. 5 is obtained based on the constant Vc. Then, the voltage correction amount V1 is calculated as a value satisfying the target current value Ip = Ip ′.

  First, the constant Vc in the equation (5) when the target current value Ip is the search center satisfies the condition that the voltage V in the equation (5) matches the voltage V in the equation (4) when the current value I = Ip. It is calculated as a value to be That is, in the equation of Vc−RI = Vo− (R + αβ) I, by substituting Ip of equation (6) for I and rearranging it, the equation of Vc = (2R + αβ) Vo / 2 (R + αβ) ( The constant Vc is obtained as 7).

  Next, the current value Ip ′ corresponding to the maximum power (power peak) indicated by the broken line in FIG. 5 is obtained by substituting Vc represented by Expression (7) into Vc in Expression (5), V = (2R + αβ) Vo. In the equation / 2 (R + αβ) −RI, it is obtained as 1/2 of the current value I satisfying V−V1 = 0. That is, the equation of V−V1 = (2R + αβ) Vo / 2 (R + αβ) −RI−V1 = 0 is arranged to obtain an equation of I = (2R + αβ) Vo / 2R (R + αβ) −V1 / R. The current value Ip ′ is obtained as / 2. This current value Ip ′ is expressed by the following equation (8): Ip ′ = (2R + αβ) Vo / 4R (R + αβ) −V1 / 2R.

  The voltage correction amount V1 for obtaining the voltage-current characteristic indicated by the broken line in FIG. 5 from the apparent dynamic characteristic indicated by the dotted line in FIG. 5 is represented by Ip in Expression (6) and Expression (8). Is obtained as a value that satisfies the condition of equalizing Ip ′. That is, the voltage correction amount V1 is obtained by arranging the equation Vo / 2 (R + αβ) = (2R + αβ) Vo / 4R (R + αβ) −V1 / 2R. This voltage correction amount V1 is expressed by an equation (9) where V1 = αβVo / 2 (R + αβ).

  Therefore, the third means of the arithmetic control unit 4 corrects the apparent dynamic characteristic shown by the dotted line and the equation (5) of V = Vc−RI in FIG. 5 with the voltage correction amount V1, thereby obtaining the target current value Ip. A correction voltage value for changing the current value of the thermoelectric power generation module 1 is obtained so as to track the maximum power (power peak) as the search center.

  In the thermoelectric power generator according to one embodiment configured as described above, when the thermoelectric power generation module 1 shown in FIG. 3 starts a power generation operation, the temperature gradient inside the thermoelectric power generation module 1 is caused by the Peltier effect associated with the power generation operation. Change. At that time, the first static means of the arithmetic control unit 4 takes the actual static characteristic of the thermoelectric power generation module 1 in consideration of the change in the temperature gradient due to the Peltier effect, that is, the actual static characteristic indicated by the solid line in FIG. Estimated as equation (4) for (R + αβ) I.

  Subsequently, the target current value Ip corresponding to the actual maximum power in the actual static characteristics of the thermoelectric power generation module 1 estimated by the first means by the second means of the arithmetic control unit 4 is Ip = Vo / 2 (R + αβ). Obtained as equation (6). Then, a correction for changing the current value of the thermoelectric power generation module 1 so that the third means of the arithmetic control unit 4 tracks the maximum power (power peak) with the target current value Ip obtained by the second means as the search center. Calculate the voltage value.

  And the correction voltage value for control which the 3rd means of the calculation control part 4 calculated is output to the current control part 5 shown in FIG. 3, and the output current of the thermoelectric power generation module 1 is changed to FIG. 4 by MPPT control. As shown, that is, the pulsating current having the target current value Ip as the average current value I (mean) is controlled.

  FIG. 6 shows a processing procedure in the arithmetic control unit 4 described above. First, in steps S1 to S4, the maximum current value I (M), the minimum current value I (m), and the maximum value shown in FIG. The voltage value V (M) and the minimum voltage value V (m) are sequentially measured.

  In the subsequent step S5, the internal resistance R by the n-type thermoelectric power generation element N and the p-type thermoelectric power generation element P is expressed by the equation R = (V (M) −V (m)) / (I (M) −I (m)). In the next step S6, the voltage correction amount V1 represented by the equation (9) of V1 = αβVo / 2 (R + αβ) is calculated.

  In step S7, the voltage value is corrected by subtracting the voltage correction amount V1 from the maximum voltage value V (M) and the minimum voltage value V (m), respectively, and the maximum power (power) is set with the target current value Ip as the search center. A correction voltage value for changing the current value of the thermoelectric power generation module 1 so as to track the peak) is obtained.

  Then, in the last step S8, the corrected voltage value obtained in step S7 is output to the current control unit 5 to execute MPTT control, and the output current of the thermoelectric power generation module 1 shown in FIG. The pulsating current is set to the value I (mean).

  Therefore, according to the thermoelectric power generation device of one embodiment, the output of the thermoelectric power generation module 1 is set to the maximum power in accordance with the actual voltage-current characteristics considering the temperature gradient change due to the Peltier effect accompanying the power generation operation of the thermoelectric power generation module 1. It can be tracked and can be configured as a highly efficient thermoelectric generator.

  The thermoelectric generator according to the present invention is not limited to the above-described embodiment. For example, the constant α determined by the material and design of the n-type thermoelectric generator N and the p-type thermoelectric generator P, and the n-type thermoelectric generator N and the p-type thermoelectric generator P, the heat receiving substrate 1A and the heat dissipation substrate 1B The invariant constant β determined by the material and design may be fixed to a value obtained by measuring the characteristics of the thermoelectric power generation module 1 in advance, or may be obtained by a device that measures the values of α and β or an algorithm that estimates. It may be a value.

It is a perspective view showing the schematic structure of the thermoelectric power generation module which constitutes the thermoelectric power generation device concerning one embodiment of the present invention. It is a figure which shows the change of the temperature gradient accompanying the electric power generation effect | action of the thermoelectric power generation module shown in FIG. It is a block block diagram of the output control system of a thermoelectric power generator provided with the thermoelectric power generation module shown in FIG. It is a graph of the pulsating current output from the current control part shown in FIG. It is a graph which shows the voltage-current characteristic of the thermoelectric power generation module shown in FIG. It is a flowchart which shows the process sequence in the calculation control part shown in FIG.

Explanation of symbols

1 Thermoelectric power generation module 1A Heat receiving substrate (high temperature side heat transfer member)
1B Heat dissipation board (low temperature side heat transfer member)
2 High heat source 3 Cooling source 4 Operation control unit 5 Current control unit 6 Voltage conversion unit

Claims (1)

A thermoelectric generator that is output-controlled to track maximum power based on the voltage-current characteristics of the thermoelectric generator module,
Means for estimating an actual voltage-current characteristic in consideration of a change in temperature gradient accompanying the power generation action of the thermoelectric power generation module;
Means for obtaining a target current value corresponding to the actual maximum power from the estimated voltage-current characteristics;
A thermoelectric generator comprising: means for obtaining a correction voltage value for changing the current value so as to follow the maximum power with the obtained target current value as a search center.

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