JP7550955B2 - Thermoelectric conversion control device and method for controlling a thermoelectric conversion device - Google Patents

Description

The present disclosure relates to a control device and a control method for a thermoelectric conversion device that converts thermal energy into electrical energy.

A conventional control device for a thermoelectric conversion device is known that matches the output voltage and output current of the thermoelectric conversion device with the internal impedance of the thermoelectric conversion device in order to maximize the power output by the thermoelectric conversion device (for example, Patent Document 1).

JP 2008-22688 A

In an ideal system in which there is no thermal resistance between the thermoelectric conversion device and the high-temperature heat source and between the thermoelectric conversion device and the low-temperature cooling source, the control device for the thermoelectric conversion device as described above is capable of obtaining the maximum output operating point of the thermoelectric conversion device (the operating point at which the output power is at its maximum) and maximizing the output power. However, in an actual system in which there is thermal resistance, there is a problem in that it is not possible to obtain the maximum output operating point and therefore it is not possible to maximize the output power.

The present disclosure has been made to solve these problems, and aims to provide a control device that can bring the output power of a thermoelectric conversion device close to its maximum value even in a system in which thermal resistance exists between the thermoelectric conversion device and a high-temperature heat source and between the thermoelectric conversion device and a low-temperature cooling source.

The thermoelectric conversion control device according to the present disclosure includes a current/voltage measuring unit that measures the current and voltage input from a thermoelectric conversion device to a power conversion unit that converts the power output by the thermoelectric conversion device, and a power conversion control unit that calculates a maximum output load resistance value, which is the load resistance value that should be connected to the output terminal of the thermoelectric conversion device in order to maximize the output power of the thermoelectric conversion device, based on the current and the voltage measured by the current/voltage measuring unit, and controls the current input from the thermoelectric conversion device to the power conversion unit so that the resistance value when the power conversion unit is viewed from the input terminal side of the power conversion unit becomes the maximum output load resistance value. The power conversion control unit changes the current input to the power conversion unit by a constant value, and calculates the maximum output load resistance value of the thermoelectric conversion device based on the difference between the voltage measured immediately after changing the current and the voltage measured after the voltage has stabilized after changing the current, and the amount of change in the current when the current is changed.

According to the present disclosure, the maximum output load resistance value of the thermoelectric conversion device can be obtained based only on electrical measurements, and the power output by the thermoelectric conversion device can be brought close to the maximum value. Therefore, even in a system in which thermal resistance exists between the thermoelectric conversion device and the high-temperature heat source and between the thermoelectric conversion device and the low-temperature cooling source, it is possible to bring the output power of the thermoelectric conversion device close to the maximum value.

The objects, features, aspects, and advantages of the present disclosure will become more apparent from the following detailed description and accompanying drawings.

1 is a configuration diagram showing a control device for a thermoelectric conversion device (thermoelectric conversion control device) according to a first embodiment. 4 is a flowchart showing the operation of the thermoelectric conversion device according to the first embodiment. FIG. 13 is a diagram showing the change in output voltage over time when the output current of the thermoelectric conversion device is changed. FIG. 11 is a diagram showing the change over time in the temperature difference between the high-temperature side and the low-temperature side of a thermoelectric conversion module when the output current of the thermoelectric conversion device is changed. 10A and 10B are diagrams for explaining the behavior of a thermoelectric converter when the output current of the thermoelectric converter is changed. 10A and 10B are diagrams for explaining the behavior of a thermoelectric converter when the output current of the thermoelectric converter is changed.

<First embodiment>
Hereinafter, a control device for a thermoelectric conversion device will be referred to as a "thermoelectric conversion control device." Fig. 1 is a diagram showing a configuration of a thermoelectric conversion control device according to a first embodiment. As shown in Fig. 1, a thermoelectric conversion control device 12 is connected between a thermoelectric conversion device 11 and a load 13, converts the power generated by the thermoelectric conversion device 11, and supplies the converted power to the load 13.

The thermoelectric conversion device 11 is a device that converts thermal energy into electrical energy, and includes a thermoelectric conversion module 11a, a high-temperature side heat exchanger 11b installed on the high-temperature side of the thermoelectric conversion module 11a, and a low-temperature side heat exchanger 11c installed on the low-temperature side of the thermoelectric conversion module 11a.

The thermoelectric conversion module 11a includes at least one thermoelectric conversion element connected between the high-temperature side and the low-temperature side. The thermoelectric conversion element is made of a thermoelectric material and generates electricity by the Seebeck effect, in which an electromotive force is generated according to the temperature difference between both ends. The power generated by the thermoelectric conversion module 11a is output from the positive output terminal and the negative output terminal of the thermoelectric conversion device 11. When the thermoelectric conversion module 11a has multiple thermoelectric conversion elements, the multiple thermoelectric conversion elements are connected in series or parallel within the thermoelectric conversion module 11a.

The high-temperature side heat exchanger 11b has the function of receiving heat from high-temperature fluids such as exhaust gas discharged from factories and transferring the heat to the high-temperature side of the thermoelectric conversion module 11a. For example, a fin-shaped structure made of aluminum or stainless steel (SUS) is used as the high-temperature side heat exchanger 11b. The low-temperature side heat exchanger 11c has the function of removing heat from the low-temperature side of the thermoelectric conversion module 11a. For example, a structure in which cooling water flows through a block made of aluminum or copper is used as the low-temperature side heat exchanger 11c. Due to the action of the high-temperature side heat exchanger 11b and the low-temperature side heat exchanger 11c, heat penetrates from the high-temperature side to the low-temperature side of the thermoelectric conversion module 11a, generating an electromotive force in the thermoelectric conversion module 11a.

The thermoelectric conversion control device 12 has a positive input terminal connected to the positive output terminal of the thermoelectric conversion device 11 and a negative input terminal connected to the negative output terminal of the thermoelectric conversion device 11, and the power output by the thermoelectric conversion device 11 is input to the thermoelectric conversion control device 12. The thermoelectric conversion control device 12 also includes a power conversion unit 12a, a current/voltage measurement unit 12b, and a power conversion control unit 12c.

The power conversion unit 12a is a conversion circuit that converts the power input from the thermoelectric conversion device 11 to the thermoelectric conversion control device 12. Either a step-up type, step-down type, or step-up/step-down type DC-DC converter is used as the power conversion unit 12a, depending on the relationship between the electromotive force of the thermoelectric conversion device 11 and the voltage required by the load 13. The circuit of the power conversion unit 12a shown in FIG. 1 is a step-down converter circuit configuration when the output voltage of the optimal operating point of the thermoelectric conversion device 11 is lower than the voltage required by the load 13. The power converted by the power conversion unit 12a is output from the positive output terminal and the negative output terminal of the thermoelectric conversion control device 12.

The load 13 has a positive input terminal connected to the positive output terminal of the thermoelectric conversion control device 12 and a negative input terminal connected to the negative output terminal of the thermoelectric conversion control device 12, and the power converted by the thermoelectric conversion control device 12 is input to the load 13. The load 13c is composed of a constant voltage source such as a storage battery.

The current/voltage measuring unit 12b is a measuring circuit that measures the current and voltage related to the power input from the thermoelectric conversion device 11 to the thermoelectric conversion control device 12. The power conversion control unit 12c is a control circuit that performs maximum output control to bring the output power of the thermoelectric conversion device 11 closer to the maximum value by controlling the power conversion unit 12a based on the current and voltage measured by the current/voltage measuring unit 12b.

The load resistance value (load resistance value between the positive input terminal and the negative input terminal) of the power conversion unit 12a as viewed from the input terminal side of the thermoelectric conversion control device 12, i.e., the value of (input voltage)/(input current), can be controlled by the duty ratio, which is the time ratio of opening and closing of the switching elements constituting the DC-DC converter of the power conversion unit 12a. For example, in the power conversion unit 12a (step-down converter) having the circuit configuration shown in FIG. 1, increasing the duty ratio of the switching elements reduces the load resistance value of the power conversion unit 12a. The power conversion control unit 12c controls the opening and closing of the switching elements by inputting a periodic rectangular wave switching signal, such as a PWM (Pulse Width Modulation) wave or a PFM (Pulse Frequency Modulation) wave, to the gate of the switching element of the power conversion unit 12a, thereby controlling the load resistance value of the power conversion unit 12a.

The thermoelectric conversion control device 12 performs maximum output control processing of the thermoelectric conversion device 11 by the power conversion control unit 12c controlling the load resistance value of the power conversion unit 12a based on the current and voltage measured by the current and voltage measurement unit 12b, i.e., the output current and output voltage of the thermoelectric conversion device 11.

The power conversion unit 12a may be an external component of the thermoelectric conversion control device 12. In other words, the thermoelectric conversion control device 12 may be configured to include only the current/voltage measurement unit 12b and the power conversion control unit 12c, and the thermoelectric conversion control device 12 may control the load resistance value of the power conversion unit 12a connected to the outside.

Below, we will explain the processing of maximum output control of the thermoelectric conversion device 11 performed by the thermoelectric conversion control device 12.

Figure 2 shows a flowchart illustrating the operation of the thermoelectric conversion control device 12. In the following description, the output current and output voltage of the thermoelectric conversion device 11 measured by the current/voltage measuring unit 12b are denoted as current I and voltage V, respectively.

When the thermoelectric conversion control device 12 starts operating, in step S10, the power conversion control unit 12c controls the duty ratio of the switching signal input to the switching element of the power conversion unit 12a so that the current I measured by the current/voltage measurement unit 12b becomes an arbitrary constant value _I1 , and waits until the fluctuation of the voltage V becomes small.

Next, in step S11, the power conversion control unit 12c changes the duty ratio of the switching signal to change the current I from _I1 to _I1 +ΔI.

Next, in step S12, the current/voltage measuring unit 12b measures the voltage V immediately after the current I is changed to _I1 + ΔI in step S11. The voltage V measured in step S12 is designated as _V1 . Here, "immediately after the current I is changed" refers to a period from when the current I is changed until a time significantly shorter than the thermal time constant of the thermoelectric conversion device 11 (e.g., 10 seconds) has elapsed. In this embodiment, step S12 is performed within 0.01 seconds after the current I is changed to _I1 + ΔI, and the voltage _V1 is measured.

The thermal time constant of the thermoelectric converter 11 causes a time delay in the thermal response of the thermoelectric converter 11, and its value is determined by the heat capacity and thermal resistance of the high-temperature heat exchanger 11b, the heat capacity and thermal resistance of the low-temperature heat exchanger 11c, and the heat capacity and thermal resistance of the thermoelectric conversion module 11a. If the thermal time constant of the thermoelectric converter 11 cannot be estimated in advance, it is preferable to change the current I and then measure the voltage _V1 as early as possible with the current-voltage measuring unit 12b.

Next, in step S13, after changing the current I, the system of the thermoelectric converter 11 is thermally stabilized and the voltage V is stabilized (fluctuations become small). The reason why the voltage V fluctuates temporarily when the current I is changed is as follows:
(1) When the current I changes and the thermal balance of the thermoelectric conversion device 11 is temporarily disrupted, the thermoelectric conversion module 11a increases the current I. (2) When the current I increases, the thermal resistance decreases due to the Peltier effect, and as a result, the temperature difference ΔT _TEG between the high-temperature side and the low-temperature side of the thermoelectric conversion module 11a also tends to decrease. (3) However, because the high-temperature side heat exchanger 11b and the low-temperature side heat exchanger 11c each have a heat capacity, there is a time delay before the temperature difference ΔT _TEG reaches the value of the thermal equilibrium state, and as a result, there is a delay in the voltage V of the thermoelectric conversion module 11a reaching the equilibrium state.

Thereafter, in step S14, the current/voltage measuring unit 12b measures the stabilized voltage V. The voltage V measured in step S14 is designated as _V2 .

3 and 4 show examples of the time change (transient characteristics) of the voltage V and the temperature difference ΔT _TEG of the thermoelectric conversion module 11a when the current I output by the thermoelectric conversion device 11 is increased by ΔI. As shown in FIG. 3, when the current I is increased by ΔI, the voltage V transitions to voltage _V1 immediately thereafter, but thereafter, the voltage V approaches voltage _V2 in accordance with the current-voltage characteristics of the thermoelectric conversion device 11 at thermal equilibrium. The time constant of the voltage V when approaching is equal to the thermal time constant of the thermoelectric conversion device 11 described above. This is because the voltage V output by the thermoelectric conversion module 11a is proportional to the temperature difference ΔT _TEG due to the Seebeck effect.

Therefore, in step S13, it is preferable to wait until at least a time equal to or greater than the thermal time constant of the thermoelectric conversion device 11 has elapsed since step S11, and it is more preferable to wait for a time of 3T or more, where T is the thermal time constant of the thermoelectric conversion device _11. When ΔI is a positive value, the voltage V gradually decreases and converges to a constant value as shown in Fig. 3, but when ΔI is a negative value, the voltage V1 gradually increases and converges to a constant value. When the thermal time constant T of the thermoelectric conversion device 11 can be obtained in advance, waiting for a time of 3T or more brings the thermoelectric conversion device 11 close to a thermal equilibrium state, and a value close to the convergence value can be obtained as the voltage _V2 .

When the voltage _V2 is measured in step S14, in step S15, the power conversion control unit 12c calculates a maximum output load resistance _Rpmax, which is a load resistance value at which the output power of the thermoelectric conversion device 11 is maximized, based on the following formula (1): In formula (1), _Rint is the internal resistance value of the thermoelectric conversion device 11 (the internal resistance value of the thermoelectric conversion module 11a).

Next, in step S16, the power conversion control unit 12c controls the duty ratio of the switching signal input to the switching element of the power conversion unit 12a so that the load resistance value seen from the input terminal side of the power conversion unit 12a becomes the maximum output load resistance value _Rpmax calculated in step S14. Specifically, the power conversion control unit 12c adjusts the duty ratio of the switching signal to control the current I so that the relationship between the voltage V and current I output by the thermoelectric conversion device 11 and the maximum output load resistance value _Rpmax becomes V/I = _Rpmax .

Next, in step S17, while controlling V/I=R _pmax , the process waits again for a certain period of time so that the thermoelectric converter 11 approaches thermal equilibrium. As with the waiting time in step S13, the waiting time in step S17 is preferably at least equal to or greater than the thermal time constant T of the thermoelectric converter 11, and more preferably equal to or greater than 3T. In this embodiment, the waiting time in steps S13 and S17 is set to 3T.

Then, in step S18, the current/voltage measuring unit 12b measures the voltage V and the current I, and calculates the power generation amount P = V x I of the thermoelectric conversion device 11.

Furthermore, the thermoelectric conversion control device 12 performs the following steps S19 to S21 to continuously track the maximum output operating point of the thermoelectric conversion device 11 even when the maximum output operating point fluctuates due to temperature changes in the heat source or cooling source.

In step S19, the process waits for an arbitrary fixed time _tm . This time _tm is a period for continuously monitoring the amount of power generated by the thermoelectric converter 11.

Next, in step S20, the current/voltage measuring unit 12b measures the voltage V and the current I, and calculates the power generation amount P' of the thermoelectric conversion device 11 at this time. If the voltage V and current I measured in step S20 are I' and V', respectively, then P' = I' x V'.

Next, in step S21, it is determined whether the power generation amount P calculated in step S18 and the power generation amount P' calculated in step S20 are different by a certain value ΔP or more. If P and P' are different by ΔP or more (YES in step S21), there is a possibility that the internal resistance value R _int or the maximum output load resistance value R _pmax of the thermoelectric conversion device 11 has changed and the maximum output operating point of the thermoelectric conversion device 11 has changed, so the process returns to step S10 and moves to a procedure of calculating the maximum output load resistance value R _pmax again. On the other hand, if the difference between P and P' is less than ΔP (NO in step S21), the process returns to step S19, and the procedure of calculating the power generation amount P' is repeatedly performed at a period of a certain time t _m while keeping the load resistance value (load resistance value of the thermoelectric conversion control device 12) applied to the thermoelectric conversion device 11 constant.

As described above, the thermoelectric conversion control device 12 according to the first embodiment obtains the maximum output operating point (maximum output load resistance value R _pmax ) of the thermoelectric conversion device 11 based only on the electrical measurement of the current I and voltage V output by the thermoelectric conversion device 11, and brings the output power of the thermoelectric conversion device 11 closer to the maximum value. Therefore, even in a system in which thermal resistance exists between the thermoelectric conversion device 11 and a high-temperature heat source and between the thermoelectric conversion device 11 and a low-temperature cooling source, it is possible to bring the output power of the thermoelectric conversion device 11 closer to the maximum value.

Here, the principle by which the maximum output load resistance value R _pmax of the thermoelectric converter 11 is obtained from the above formula (1) will be described.

In an ideal state in which there is no thermal resistance between the thermoelectric conversion module 11a and the high-temperature fixed point and between the thermoelectric conversion module 11a and the low-temperature fixed point, the maximum output load resistance value R _pmax of the thermoelectric conversion module 11a coincides with the internal resistance value R _int of the thermoelectric conversion module 11a. This is due to the maximum power supply theorem.

On the other hand, as shown in Fig. 5, when thermal resistance exists between the thermoelectric conversion module 11a and the high-temperature fixed point and between the thermoelectric conversion module 11a and the low-temperature fixed point, the maximum output load resistance value _Rpmax of the thermoelectric conversion module 11a is higher than the internal resistance value _Rint of the thermoelectric conversion module 11a. The maximum output load resistance value _Rpmax in this case is derived as follows.

If the Peltier coefficient of the thermoelectric conversion module 11a is Π, the amount of heat Q penetrating the thermoelectric conversion module 11a when a current I flows through the thermoelectric conversion module 11a increases by ΠI due to the Peltier effect compared to when the current I = 0. Therefore, if the amount of heat penetrating the thermoelectric conversion module 11a when the current I = 0 is _Q0 , the amount of heat penetrating the thermoelectric conversion device 11 is expressed by the following formula (2).

The temperature difference between the temperature Th of the high-temperature side temperature fixed point and the temperature Tc of the low-temperature side temperature fixed point is ΔT0. The high-temperature side temperature fixed point is the temperature of the thermal fluid flowing through the high-temperature side heat exchanger 11b, and the low-temperature side temperature fixed point is the temperature of the cooling water flowing through the low-temperature side heat exchanger 11c. As shown in Fig. 5, the thermal resistance between the high-temperature side temperature fixed point and the high-temperature side surface of the thermoelectric conversion device 11 is _{Rth_h} , the thermal resistance between the low-temperature side temperature fixed point and the low-temperature side surface of the thermoelectric conversion module 11a is _{Rth_c} , and the sum of _{Rth_h} and _{Rth_c} is the additional heating resistance _{Rth_add} .

The temperature difference ΔT _TEG between the high temperature side surface and the low temperature side surface of the thermoelectric conversion module 11a is expressed by the following formula (3) using Q in formula (2).

When the Seebeck coefficient S and the internal resistance value R _int of the thermoelectric conversion module 11a are used, the output voltage V of the thermoelectric conversion module 11a is expressed by the following formula (4).

By substituting equations (2) and (3) into equation (4), we obtain the following equation (5).

Here, the output power P of the thermoelectric conversion module 11a is expressed by the following equation (6).

By substituting equation (5) into equation (6), we obtain the following equation (7).

Since P in equation (7) is a quadratic function of I, the value _Ipmax of the current I when the output power P of the thermoelectric conversion module 11a becomes maximum can be obtained as the maximum extreme value point of the upward convex quadratic function, and can be expressed by the following equation (8).

Moreover, the voltage V _pmax at this time can be expressed by the following equation (9) by substituting equation (8) into equation (4).

From equations (8) and (9), the maximum output load resistance value R _pmax of the thermoelectric conversion module 11 a can be expressed by the following equation (10).

As can be seen from equation (10), the maximum output load resistance value R _pmax of the thermoelectric conversion module 11 a is higher than the internal resistance value R _int by SΠR _{th — add} .

Next, the principle of acquiring SπR _{th_add} based only on the measurement of the current I and the voltage V output by the thermoelectric conversion module 11a without performing thermal measurement will be described.

3 and 4, as well as 5 and 6, the temperature difference ΔT _TEG of the thermoelectric conversion module 11a when the voltage V= _V1 is set to _ΔT1 , and the temperature difference ΔT _TEG of the thermoelectric conversion module 11a when the voltage V= _V2 is set to _ΔT2 . In maximum output control of the thermoelectric conversion device 11, the difference ΔT ₁ -ΔT ₂ of the temperature difference ΔT _TEG of the thermoelectric conversion module 11a can be calculated from the difference between V1 and _V2 using the Seebeck effect formula _{. The difference ΔT 1 -ΔT 2} is expressed by the following formula (11).

Furthermore, if the amount of heat passing through the thermoelectric conversion module 11a when I=I ₁ +ΔI is Q ₀ +ΔQ, ΔQ is expressed by the following formula (12).

Here, when I= _I1 +ΔI, the temperature difference occurring at the heating resistor _{Rth_add} increases by _{Rth_addΔQ} in a steady state compared to when I= _I1 . However, in a transient state, the temperature difference occurring at _{Rth_add} immediately after the current I is changed by ΔI remains the same _{Rth_addQ} as it was immediately before the change in current I because the temperature immediately before the change in current I is maintained by the heat capacity, and the temperature difference occurring at _{Rth_add} after a certain time has passed increases by _{Rth_addΔQ} compared to when I= _I1 . This is equal to _ΔT1 - _ΔT2 , which is the change in the temperature difference ΔT _TEG of the thermoelectric conversion element, so the following equation (13) holds.

By substituting equations (11) and (12) into equation (13), we obtain the following equation (14).

Furthermore, by substituting equation (14) into equation (10), S and Π are eliminated and the following equation (15) is obtained.

Therefore, when the internal resistance value R _int of the thermoelectric conversion module 11a is known in advance, the maximum output load resistance value R _pmax can be calculated based on the results of electrical measurement without performing thermal measurement.

<Embodiment 2>
In the second embodiment, when the power conversion control unit 12c controls the current I to a constant value _I1 in step S10 of the flowchart in FIG. 2, the thermoelectric conversion module 11a is put in an open state to set the current _I1 to 0, and when the current I is changed by ΔI in step S11, the thermoelectric conversion module 11a is put in a short-circuit state to set ΔI to the current value _Isc when the thermoelectric conversion module 11a is short-circuited.

This allows V ₁ -V ₂ and ΔI to be as large as possible without using an external electromotive force, and the maximum output load resistance value R _pmax can be obtained with high accuracy from equation (1), making it possible to bring the power generation amount P of the thermoelectric conversion device 11 close to the maximum value with high accuracy.

<Third embodiment>
In the third embodiment, the power conversion control unit 12c is configured to calculate the internal resistance value R _int of the thermoelectric conversion module 11a based on the current I and voltage V measured by the current/voltage measurement unit 12b when the load resistance value seen from the input terminal side of the power conversion unit 12a is changed. The internal resistance value R _int of the thermoelectric conversion module 11a can be calculated by dividing the amount of change in voltage V when the load resistance value of the power conversion unit 12a is changed by the amount of change in current I. This allows the power conversion control unit 12c to obtain the accurate internal resistance of the thermoelectric conversion module 11a after the temperature has stabilized, and makes it possible to monitor the accurate state of the thermoelectric conversion module 11a.

The internal resistance value R _int of the thermoelectric conversion module 11a can be obtained from the current I and the voltage V at two or more measurement points (measurement times) in the thermoelectric conversion module 11a that is stable in terms of temperature. For example, in step S10 in Fig. 2, if the current I is controlled to a constant value _I1 and then the voltage V is stabilized, and the current/voltage measurement unit 12b measures the value V0 (see Fig. 3) of the voltage V at that time, the power conversion control unit 12c can calculate the internal resistance value R _int by the following formula (16) and apply it to formula (15) when calculating the maximum output load resistance value R _pmax using formula (15) in step S15.

<Fourth embodiment>
In the fourth embodiment, the power conversion control unit 12c is configured to calculate the thermal time constant T of the thermoelectric conversion device 11 when changing the load resistance value seen from the input terminal side of the power conversion unit 12a. The calculated thermal time constant T can be used to determine the waiting time in steps S13 and S17 in FIG. 2, for example.

For example, between changing the current I in step S11 of FIG. 2 and stabilizing the voltage V in step S13, the power conversion control unit 12c can obtain the thermal time constant T by the following processing.

First, during a period from when the current I is controlled to _I1 + ΔI in step S11 until an arbitrary time has elapsed, the current/voltage measurement unit 12b measures the current I and the voltage V at three or more measurement points (measurement times). The measurement points may include the measurement point of step S12 and the measurement point of step S14. Therefore, the current/voltage measurement unit 12b only needs to measure the current I and the voltage V at at least one measurement point other than steps S12 and S14 during the period from step S12 to step S14.

For example, if the time t at which the voltage _V1 is measured in step S12 is set to 0, the change in voltage V with respect to time t can be expressed by the following equation (17) using the voltage _V1 measured in step S12, the voltage _V2 measured in step S14, and the thermoelectric conversion device 11.

By substituting the voltage V measured at a measurement point other than step S12 and step S14 and the time t into equation (17), the thermal time constant T of the thermoelectric conversion device 11 can be obtained.

In addition, when the voltage V is measured at four or more measurement points, the thermal time constant T may be calculated by determining the transient characteristics of the voltage V using the least squares method or the like.

The electromotive force of the thermoelectric conversion device 11 is proportional to the temperature difference ΔT between the high-temperature side and the low-temperature side of the thermoelectric conversion module 11a due to the Seebeck effect (V = SΔT). Therefore, the time response of the voltage V shows the same behavior as the time response of the temperature difference ΔT. Because of this, the thermal time constant T of the voltage V can be regarded as the thermal time constant T as it is, so it is possible to obtain the thermal time constant T by measuring only the voltage V.

Therefore, in this embodiment, the thermoelectric conversion control device 12 can obtain the thermal time constant of the thermoelectric conversion device 11 through electrical measurement alone without adding any additional thermal measurement hardware such as a thermocouple, and the output power of the thermoelectric conversion device 11 can be brought close to its maximum value in an inexpensive and simple manner.

In addition, it is possible to freely combine each embodiment, and to modify or omit each embodiment as appropriate.

It is understood that the above description is illustrative in all respects and that countless variations not illustrated may be envisaged.

11 thermoelectric conversion device, 11a thermoelectric conversion module, 11b high temperature side heat exchanger, 11c low temperature side heat exchanger, 12 thermoelectric conversion control device, 12a power conversion unit, 12b current and voltage measurement unit, 12c power conversion control unit, 13 load.

Claims (11)

a current/voltage measuring unit that measures a current and a voltage input from a thermoelectric converter to a power converter that converts the power output from the thermoelectric converter;
a power conversion control unit that calculates a maximum output load resistance value, which is a load resistance value to be connected to an output terminal of the thermoelectric conversion device in order to maximize the output power of the thermoelectric conversion device, based on the current and the voltage measured by the current/voltage measurement unit, and controls the current input from the thermoelectric conversion device to the power conversion unit so that the resistance value of the power conversion unit as viewed from the input terminal side of the power conversion unit becomes the maximum output load resistance value;
Equipped with
the power conversion control unit changes the current input to the power conversion unit by a constant value, and calculates the maximum output load resistance value of the thermoelectric conversion device based on a difference between the voltage measured immediately after the current is changed and the voltage measured after the voltage is stabilized after the current is changed, and an amount of change in the current when the current is changed.
Thermoelectric conversion control device. the power conversion control unit changes the thermoelectric conversion device from an open state to a short-circuit state when changing the current input to the power conversion unit;
The thermoelectric conversion control device according to claim 1 . the current/voltage measuring unit measures the current and the voltage input to the power conversion unit at two or more points,
the power conversion control unit calculates the maximum output load resistance value of the thermoelectric conversion device based on an internal resistance value of the thermoelectric conversion device calculated from measurement results of the current and the voltage at two or more points;
The thermoelectric conversion control device according to claim 1 or 2. If the voltage measured immediately after the change in the current is V ₁ , the voltage measured after the voltage has stabilized is V ₂ , the amount of change in the current is ΔI, and the internal resistance value of the thermoelectric conversion device is R _int , the power conversion control unit calculates the maximum output load resistance value R _pmax of the thermoelectric conversion device as follows:
R _pmax = R _int + (V ₁ - V ₂ )/ΔI
The calculation is performed using the following relation:
The thermoelectric conversion control device according to any one of claims 1 to 3. the power conversion control unit calculates a thermal time constant of the thermoelectric conversion device from the measurement results of the current and the voltage at three or more points, and determines a waiting time until the voltage stabilizes after changing the current based on the calculated thermal time constant.
The thermoelectric conversion control device according to any one of claims 1 to 4. The power conversion unit is further provided.
The thermoelectric conversion control device according to any one of claims 1 to 5. (a) changing, by a constant value, a current input from a thermoelectric converter to a power converter that converts the power output from the thermoelectric converter;
(b) measuring the current and voltage input from the thermoelectric converter to the power converter immediately after the step (a);
(c) measuring the current and the voltage input from the thermoelectric converter to the power converter after the voltage has stabilized after the step (b);
(d) calculating a maximum output load resistance value, which is a load resistance value to be connected to an output terminal of the thermoelectric conversion device in order to maximize the output power of the thermoelectric conversion device, based on a difference between the voltage measured in the step (b) and the voltage measured in the step (c) and an amount of change in the current in the step (a);
(e) controlling the current input from the thermoelectric converter to the power conversion unit so that a resistance value of the power conversion unit as viewed from an input terminal side of the power conversion unit becomes the maximum output load resistance value;
A control method for a thermoelectric conversion device comprising: In the step (a), when the current input to the power conversion unit is changed, the thermoelectric conversion device is changed from an open state to a short-circuit state.
A method for controlling a thermoelectric conversion device according to claim 7. (f) measuring the current and the voltage input to the power conversion unit at two or more points;
Including,
In the step (d), the maximum output load resistance value of the thermoelectric conversion device is calculated based on an internal resistance value of the thermoelectric conversion device calculated from measurement results of the current and the voltage at two or more points.
A method for controlling the thermoelectric conversion device according to claim 7 or 8. In the step (d), the voltage measured immediately after the change in the current is denoted as V ₁ , the voltage measured after the voltage has stabilized is denoted as V ₂ , the amount of change in the current is denoted as ΔI, and the internal resistance value of the thermoelectric converter is denoted as R _int . Then, the maximum output load resistance value R _pmax of the thermoelectric converter is given by:
R _pmax = R _int + (V ₁ - V ₂ )/ΔI
It is calculated using the following relation:
A method for controlling the thermoelectric conversion device according to any one of claims 7 to 9. (g) calculating a thermal time constant of the thermoelectric conversion device from the measurement results of the current and the voltage at three or more points;
Further equipped with
The waiting time until the voltage is stabilized in the step (d) is determined based on the thermal time constant calculated in the step (g).
A method for controlling the thermoelectric conversion device according to any one of claims 7 to 10.

Images