KR101397421B1 - Temperature control system for thermoelectric element - Google Patents

Abstract

A thermoelectric element temperature control system according to the disclosed present invention comprises: a main controller (100) for generating a control signal on whether a power is supplied or not and whether the power is supplied in a normal or a reverse direction in order to adjust the temperature of a target object to the set temperature; a power supply module (200) for converting a voltage of a AC power into a DC voltage, controlling a size of the voltage according to the control signal generated by the main controller (100) and outputting the controlled voltage; a polarity switching module for normally or reversely switching a polarity of the voltage, outputted from the power supply module (200) according to the control signal of the main controller (100); and a thermoelectric module (500) installing a heat exchange (600) connected to the target object at one side and a heat radiator (700) at the other side and having a plurality of thermoelectric elements for making both sides induce an exothermic reaction or an endothermic reaction by using the power supplied from the power supply module (200) via the polarity switching module (300). The main controller (100) calculates a value of electromotive force generated according to a drive condition of the thermoelectric module (500) within a regular output range set near a polarity switching point and performs a control operation to output an on/off value for the electromotive force in an area where a dead zone dependent on the calculated electromotive force may be avoided and to output a linear value for the electromotive force in the remaining area.

Description

{Temperature Control System for Thermoelectric Element}

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a temperature control system for a thermoelectric element, and more particularly, to a temperature control system for a thermoelectric element that uses a thermoelectric module as a source for heating and cooling in various temperature control applications, Temperature control system.

A thermoelectric module (TEM) is an electronic component capable of functioning as a cooling system or a heat pump. The thermoelectric module includes a plurality of thermoelectric elements (or thermoelectric elements) capable of directly converting thermal energy into electric energy, Semiconductors) are disposed so that heat is absorbed or radiated through both sides by the polarity switching of the supplied power source. The thermoelectric module can precisely control the temperature to 0.01 ° C by controlling the supplied voltage or current, and since there is no driving part for operating the device, there is no vibration noise and it is used as the thermoelectric characteristic of the thermoelectric element. System, it is widely applied in various industrial fields and has been developed for its application.

In general, a system for controlling a temperature set by using a thermoelectric module in various temperature control fields includes a main controller for applying a control signal to the thermoelectric module, A control system composed of a voltage supply device for controlling the magnitude of the voltage in accordance with a control signal applied from the main controller and a polarity switching module for switching the voltage to positive or negative, And various types of thermoelectric modules for receiving cooling and heating outputs for controlling the temperature of the target object (fluid or solid) supplied with the applied power.

The temperature control system using the conventional thermoelectric module merely uses a thermoelectric module as a cooling source and a heating source, which is a separate heater, is applied as a heating source, so that the structure of the temperature control system as a whole becomes complicated and large, However, there is a problem that precision control is not easy and maintenance is difficult.

As a result of these problems, it has been studied how a thermoelectric module functions not only as a cooling source but also as a heating source.

The PID calculation method is commonly applied to the controller for the temperature control, and a digital output method or an analog output method is used to convert the operation result to the control output, and a power supply (SMPS: Switching Mode Power Supply ) Of the output signal. In the case of thermoelectric modules, the amount of cooling and heating output is controlled according to the amount of power applied from a power supply (SMPS). In order to obtain the output of cooling or heating using a thermoelectric module as a single source, The polarity switching of the power source applied to the module is utilized.

First, FIG. 1 shows a power supply application state when the polarity is switched by the on / off method in the conventional temperature control system. In this case, the digital output method of ON / OFF control or PWM control The voltage supplied to the thermoelectric module (TEM) 51 from the polarity switching unit 30 including the power supply unit SMPS forms a plurality of pulses in accordance with the control signal of the controller 10 If the voltage is applied in this form, the thermal stress caused by the power noise and on / off of the thermoelectric module 51 increases and accumulates to break the insulation characteristic or gradually increase the internal resistance, thereby damping the thermoelectric characteristics. The problem of falling occurs.

In view of such problems, Korean Patent No. 817419 (a temperature control system of a semiconductor manufacturing facility using a polarity switching of a thermoelectric element) discloses a technique of applying a power supply to a thermoelectric module by a linear control (Proportional Control) Lt; / RTI > Fig. 2 shows a power supply application state when polarity is switched by linear control by an analog signal in the above-described temperature control system. According to this, since the output amount of the voltage applied to the thermoelectric module 51 is varied by linear control, the thermal stress is small to prevent the insulation breakdown and characteristic damping, thereby improving the durability and reliability of parts.

However, in the case of the analog output method, the voltage applied to the thermoelectric module converges to a substantially zero value in the vicinity of the polarity switching point, and when there is a temperature deviation between both sides of the thermoelectric module in a certain period of convergence, The output does not actually react to the cooling output or the heating output. If the electromotive force is greater than the voltage applied to the thermoelectric module by the control output under the seebeck effect condition caused by the temperature deviation on both sides of the thermoelectric module, as shown in FIG. 3, (Dead zone or dead band) in which the control output does not actually react to the cooling output or the heating output at the time of the switching period (polarity switching period). Therefore, precise temperature control becomes difficult in a certain section where the dead zone is formed. Particularly, in the constant temperature control field of semiconductors and LEDs, in which very precise temperature control is required, such problems are becoming important problems.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has an advantage of a linear control method applied to stabilize durability and reliability of a component in a temperature control method using a thermoelectric element, And an object of the present invention is to provide a thermoelectric-element temperature control system that further improves the control accuracy even under the condition of generation of an electromotive force caused by a temperature difference between a heat-generating side surface and a heat-absorbing side surface.

In order to achieve the above object, a thermoelectric-element temperature control system according to the present invention comprises a main controller 100 for applying a control signal for determining whether a power source is supplied or not, A power supply module 200 for converting the voltage of the AC power source to DC, adjusting the magnitude of the voltage according to the control signal applied from the main controller 100, and outputting the adjusted voltage; A polarity switching module 300 for switching the polarity of a voltage output from the power supply module 200 according to a control signal of the main controller 100 to a positive or negative polarity and outputting the polarity; And a heat exchanger 600 connected to the target object on one side and a heat dissipating device 700 on the other side and having a plurality of thermoelectric elements and electrically connected to the power supply module 200 The thermoelectric module 500 includes a thermoelectric module 500 having both ends thermally or thermally reacted by a power source supplied from the main controller 100, And a control is made so that an output can be made in an ON / OFF manner in an area in which a dead zone according to the calculated electromotive force can be avoided, and in a range other than that, And outputs the control signal.

Meanwhile, the main controller 100 determines a difference (? (Th-Tc)) between temperature values received from the temperature sensors 610 and 710 installed in the heat exchanging device 600 and the heat dissipating device 700, The value of the electromotive force is calculated by applying a value of a setback coefficient (Seebeck coefficient,?).

In addition, the main controller 100 controls the ON / OFF control period of the linear control period or the boundary point of the output to be switched from the ON / OFF control period to the linear control period, Within the range where the absolute value of the control output is equal to or smaller than the absolute value of the calculated electromotive force.

As described above, according to the present invention, the constant output range (the voltage section having a potential higher than the electromotive force generated by the temperature difference on both sides) is preset in the vicinity of the polarity change point, that is, in the voltage range in which the characteristics of the thermoelectric elements start to occur , Calculates the electromotive force generated according to the characteristics of the thermoelectric module within the predetermined output range, recognizes the area where the dead zone according to the calculated electromotive force can be avoided, and outputs the control output applied to the thermoelectric module as an on / off control method And in the range other than that, the output is regulated by dividing it into a linear control method. Therefore, it is possible to improve the durability, control accuracy and energy efficiency of the thermoelectric module by utilizing the advantages of the conventional linear control, and avoid the dead zone generated when the linear control is applied in the section where the control output voltage by the electromotive force is lost There is an advantage that the amount of output can be controlled. As a result, according to the present invention, the durability of the thermoelectric module can be maintained and the accuracy of temperature control in the entire output section can be further improved. It also has the effect of improving the energy efficiency.

FIG. 1 is a view showing a power application state when polarity is switched by an on / off method in a conventional temperature control system,
FIG. 2 is a view showing a power application state when polarity is switched by a linear control method in a conventional temperature control system,
3 is a graph illustrating the occurrence of a dead zone in a polarity switching period in a conventional temperature control system,
4 is a block diagram of a thermoelectric-element temperature control system according to an embodiment of the present invention.
5 is a view for explaining a heat flow direction in a state where power is connected to a thermoelectric element to explain a Peltier effect,
FIG. 6 is a graph showing a COP curve of a thermoelectric element, and is a graph illustrating a section to which the present invention is applied,
FIG. 7 is a graph for explaining the remedy operation of the thermoelectric-element temperature control system of the present invention.

These and other objects, features and other advantages of the present invention will become more apparent by describing in detail preferred embodiments of the present invention with reference to the accompanying drawings. Hereinafter, a thermoelectric-element temperature control system according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 4, a thermoelectric-element temperature control system according to an embodiment of the present invention includes a main controller 100, a power supply module 200, a polarity switching module 300, and a thermoelectric module 500.

Specifically, the main controller 100 compares the temperature of the object to be cooled or heated by the thermoelectric module 500 with the temperature to be set, and determines whether the object is cooled or heated And applies a control signal to the power supply module 200 and the polarity switching module 300 regarding whether or not the voltage is supplied, and the magnitude and the reverse direction of the voltage. When the temperature control is not required, the supply of the voltage is stopped, and when the temperature control is required, the control signal for supplying the voltage is applied.

On the other hand, the main controller 100 divides the control output into an on-off control method and a linear control method to control the output. That is, the main controller 100 calculates the value of the electromotive force generated in accordance with the driving condition of the thermoelectric module 500 within a predetermined constant output range, that is, within a preset predetermined interval near the polarity switching point, It recognizes an area which avoids a dead zone or dead band of the output and controls the ON / OFF output and the polarity switching to operate in that area. Then, the main controller 100 controls the linear output to be performed in a section other than the on / off control period (see FIG. 7).

The manner in which the main controller 100 recognizes the boundary points between the on-off control period and the linear control period output is as follows. The main controller 100 calculates temperature values of the temperature sensors 610 and 710 provided in the heat exchanger 600 and the heat dissipater 700. The main controller 100 calculates the value of the electromotive force within a predetermined constant output range, (Th-Tc) of the temperature value received from the thermoelectric module and the set Seebeck coefficient? Of the thermoelectric module to calculate the value of the electromotive force. On the other hand, in the dead zone, the control output is generated when the value of the control output is equal to or smaller than the electromotive force value of the thermoelectric module in the vicinity of the polarity change point. Therefore, in order to avoid this, the main controller 100 determines whether the control output value is equal to the electromotive force A boundary point between the on-off control period and the linear control period output is determined in a range not equal to or less than the predetermined range.

For example, it is assumed that the control output is arbitrarily in the range of -100% to + 100%, and -20% to + 20% or -30% to + 30% depending on the input condition (design specification) is given to the main controller 100 When the constant output range is set, the temperature difference is recognized within the predetermined constant output range, and the temperature difference and the whitening coefficient are applied to calculate the direction and magnitude of the electromotive force. Then, it automatically recognizes the boundary point that applies the power supply to the on / off control of the digital output method within the range where the absolute value of the control output is equal to or less than the absolute value of the calculated electromotive force, The polarity switching boundary point is controlled to be varied. On the other hand, the main controller 100 stops the on / off repetitive output for controlling the PWM output amount in the interval other than the on / off output period and fixes the ON output. In other words, the PWM output control operates with a constant frequency in the ON / OFF repetitive operation to adjust the ON time and the OFF time. In the interval other than the ON / OFF output, the PWM control output is stopped. So that the control amount is calculated through the PID operation and the linear output is controlled so as to adjust the amount of output according to the amount of control.

The power supply module (SMPS) 200 converts the voltage of the AC power source to DC, adjusts the voltage level according to the control signal applied from the main controller 100, converts the voltage into a square wave, . Meanwhile, the power supply module 200 applies a power supply to the thermoelectric module in an output range other than the predetermined output range according to a control signal of the main controller, as an analog output type linear control (Proportional Control). In the linear control method, the voltage is calculated by the PID calculation method and the signal is applied. Accordingly, the main controller 100 calculates the control amount through the PID calculation and transmits the control amount to the power supply module 200, The supply module 200 adjusts the amount of output according to the amount and supplies the adjusted amount to the polarity switching module 300.

The polarity switching module 300 switches the voltage output from the power supply module 200 to positive or negative according to a control signal of the main controller 100 and outputs a controlled current to output a rectified voltage Is applied to the thermoelectric module (500) to allow the thermoelectric module (500) to perform an endothermic or exothermic reaction.

The thermoelectric module 500 is composed of a plurality of thermoelectric elements or a group of thermoelectric modules and absorbs heat or dissipates heat through both sides according to a positive or negative voltage applied from the polarity switching module 300. On both sides thereof, Devices or parts, heat dissipation devices (air-cooled or water-cooled), and the like. For example, as shown in FIG. 4, a heat exchanger 600 connected to an object to be cooled and heated is installed on one side of the thermoelectric module 500, and a heat dissipation device 700 Can be installed. However, the present invention is not limited thereto. For example, the thermoelectric module 500 may be installed on one side of the thermoelectric module 500 so that the object of interest may be directly attached thereto. The thermoelectric module according to the present invention and the heat exchanging device, parts, and objects to be connected or connected to the thermoelectric module may have various structures and configurations, and the present invention is not limited to a specific structure or configuration. When a positive voltage is applied to the thermoelectric module (thermoelectric element), one side performs an endothermic function to cool the refrigerant or target object of the heat exchange device attached to the one side, and the other side performs a heat- The heat is dissipated to the outside through the heat dissipation device. When a reverse voltage is applied to the thermoelectric module, one side performs a heat dissipation function to heat a refrigerant or a target object of the heat exchanger installed on the one side, and the other side performs an endothermic function.

Temperature sensors 610 and 710 are installed in each of the heat exchanging device 600 and the heat dissipating device 700 attached to both sides of the thermoelectric module 500. The main controller 100 receives temperature information from the temperature sensors. As described above, the main controller 100 calculates the difference (? Th-Th) between the temperature values received from the temperature sensors 610 and 710 and the set Seebeck coefficient of the thermoelectric element of the thermoelectric module 500, To calculate a value of the electromotive force and to calculate a boundary point which is switched from the linear control period to the ON control OFF period or from ON ON OFF control period to the linear control period . The characteristic of the thermoelectric material can be generally evaluated by the figure of merit (Z) expressed by the following formula (1).

[Formula 1]

 Z = α σ / κ

From here,

α: Seebeck coefficient, σ: electrical conductivity, and κ: thermal conductivity.

That is, the larger the figure of merit of the thermoelectric material is, the higher the potential difference generated becomes, and therefore, the thermoelectric material exhibits excellent characteristics. Therefore, it is preferable to use a material having a high Seebeck coefficient and electrical conductivity and a low thermal conductivity for application as a thermoelectric material from the above-mentioned [Formula 1], and it is preferable that the shape and porosity of the material, the carrier concentration, It is possible to optimize it according to the bonding strength and the like.

On the other hand, the Seebeck coefficient can be expressed by the following equation (2).

[Formula 2]

α = V / ° C.

That is, the whiteness coefficient indicates the value of the generated voltage according to the temperature difference of the thermoelectric material, and it depends on the thermoelectric material.

5 is a view for explaining the direction of heat flow according to the direction of current in a state where a DC power source is connected to a thermoelectric element. Here, the amount of heat to be transferred varies depending on the magnitude of the voltage, and the magnitude of the temperature deviation between the A-plane and the B-plane (both sides of the thermoelectric element) also changes. When the voltage of the DC power supply is 0 (zero) in the drawing, when there is a temperature difference between the A side and the B side, an electromotive force is generated in reverse. This is called a Seebeck effect. When the temperature of the A side is higher than the temperature of the B side, the current has the same direction as the arrow direction shown in the drawing. When the temperature of the A side is lower than the temperature of the B side, a current is generated in the direction opposite to the arrow direction shown. Also, as the temperature variation increases, the magnitude of the generated DC voltage increases.

For example, in order to implement the temperature control using the B-plane in a state where the temperature of the A-plane is maintained at 20 ° C, the magnitude (voltage) and the direction of the current are adjusted. In this case, when applying the method of adjusting the maximum voltage determined in the zero voltage by applying the linear control in the current supply method, there is a temperature difference between the A side and the B side, and the control output has a polarity When applied to a thermoelectric element (thermoelectric module) with a low voltage output including conversion, the dead zone (Dead Zone) in which the control output is canceled in accordance with the magnitude of the electromotive force generated by the temperature difference between the A- or Dead Band) is formed. On the other hand, since the DC voltage supplied from the digital method (ON / OFF control) is a method of adjusting the supply amount with a constant potential difference being set, the dead band due to the electromotive force generated by the Seebeck effect generated in the above- This is because it is controlled with a potential difference higher than the magnitude of the electromotive force generated by the temperature deviation.

6 is a graph showing a curve of a coefficient of performance (Z = COP) of a thermoelectric element. In the case of thermoelectric elements, the figure of merit shows a remarkable difference according to the section to be applied. In order to achieve the best cooling performance, a high voltage section is used, but the figure of merit (Z = COP) is the lowest point. Therefore, it is effective to utilize a section having a high performance index on a performance curve as needed. According to the present invention, a section using an on-off control method uses a performance index, that is, a section having a high energy efficiency.

As described above, according to the present invention, the vicinity of the polarity switching point is set to a constant output range, and the output is controlled by dividing the control output applied to the thermoelectric module within the constant output range into a linear control method or an on-off control method. In other words, the output control is performed by a linear control method in a period other than the period in which the voltage is gradually increased while the on / off control is performed based on the boundary point within a constant output range in which the voltage is low, It is possible to control the amount of output while avoiding the dead zone that occurs when the linear control is applied to the interval. As a result, the thermoelectric-element temperature control system according to the present invention can advantageously improve the durability and energy efficiency of the thermoelectric device by utilizing the advantages of the linear control and improve the accuracy of the temperature control in the entire output section.

A specific operation of the thermoelectric-element temperature control system according to the embodiment of the present invention will be described by way of example.

First, the control condition is as follows. The whitening factor (α) of the applied thermoelectric element is 0.05 V / K, and the thermoelectric module is composed of 10 series circuits. The temperature Th of the heat dissipating device is a condition of maintaining a temperature of 20 占 폚 in a water-cooled structure, and the direction of control output and current for cooling the temperature Tc of the heat exchanger is defined as a cooling output and a forward direction. That is, SV = Tc. The control output of the main controller 100 is variably changed from -100 Vdc to +100 Vdc in the range of -100% to +100%, and the constant output range is set to -20% to + 20% of the control output. Let's look at the control logic when the temperature of SV is -10 ℃, 20 ℃ and 50 ℃ respectively.

On the other hand, the magnitude and direction of the electromotive force generated in the thermoelectric module when Tc is -10 ° C, 20 ° C, and 50 ° C in the above conditions are as follows. Assuming that the Tc is -10 ° C and the stabilization condition is the no-load state, the output of the main controller 100 is the cooling output, and the direction of the electromotive force generated in the thermoelectric module is forward, The generated electromotive force is 0.05 x 10 x 30 = 15V. Assuming that the Tc is 20 ° C and the stabilization condition is also no load, the direction of the electromotive force generated in the thermoelectric module is non-directional, and the electromotive force generated by the condition of Th-Tc is 0.05 × 10 × 0 = 0 V . On the other hand, assuming that Tc is 50 ° C, the output of the main controller 100 is a heating output, assuming a stabilizing condition in a no-load state, and the direction of the electromotive force generated in the thermoelectric module is reverse. The generated electromotive force is 0.05 x 10 x 30 = -15V.

Therefore, when the control output of the main controller 100 is in the + 12V state in a state where the temperature of Th is constant at 20 占 폚 and the SV (Tc) is 20 占 폚 and disturbance (heating and cooling load) The control logic under the condition of changing from 50% to -30% is as follows. The main controller 100 generates a primary disturbance (heating load) in a state in which the control output is maintained at the cooling output + 25% in the stabilized state, regulates the output in a linear control manner up to + 50% (50V) Secondary disturbance (cooling load) is generated and the control output changes from + 50% to + 20.1% linear control output. The linear output is maintained to 0% (0V) by applying the calculated value (0.05 × 10 × 0 = 0V) from the range of + 20.0% and the polarity switching is performed based on 0% (0V) And the heating output reaches -30%. That is, it recognizes the condition that the electromotive force does not occur, and keeps the output section excluding the polarity change point as a linear output as a whole.

7, when the temperature of Th is constant at 20 DEG C and the SV (Tc) is -10 DEG C, disturbances (heating and cooling loads) are generated in the controlled object in the stabilized state, ) Control output changes from + 50% to -30%, the control logic will be described as follows. The main controller 100 generates a primary disturbance (heating load) in a state in which the control output is maintained at the cooling output + 35% in the stabilized state, adjusts the output in a linear control manner up to + 50% (50V) Secondary disturbance (cooling load) is generated and the control output changes from + 50% to + 20.1% linear control output. (A + A × 0.1 = 1) where the absolute value of the control output is less than or equal to the absolute value of the electromotive force by applying the calculated value of the electromotive force (0.05 × 10 × 30 = 15V) 15 + 15 × 0.1 = 16.5, where A is the linear power output up to +16.5% (+ 16.5V), which is the calculated electromotive force with the temperature difference of Tc and Th) OFF output, and the polarity is switched corresponding to the cooling load, and the ON / OFF output is maintained at the heating output -16.4% point. From then on, linear control is applied to reach -30%. In other words, it recognizes the condition of EMF generation and responds to ON / OFF and polarity switching instead of linear output in a certain output range. Here, the value of A multiplied by " 0.1 " means that the absolute value of the control output is not less than or equal to the absolute value of the electromotive force, that is, a value for setting a large point. .

Referring to FIG. 7, when the temperature of Th is constant at 20 ° C and the SV (Tc) is 50 ° C, the disturbance (cooling and heating load) The control logic under the condition that the control output of the control circuit changes from -50% to + 30% is as follows. The main controller 100 generates a primary disturbance (cooling load) in a state in which the control output is maintained at a heating output of -25% in the stabilized state and controls the heating output in a linear control manner up to -50% (-50V) , The secondary output (heating load) is generated, and the control output changes from -50% to -20.1% to the linear control output. (A + A × 0.1 = 15) where the absolute value of the control output is less than or equal to the absolute value of the electromotive force by applying the calculated value (0.05 × 10 × -30 = -15V) + 16 × 0.1 = 16.5, where A is the calculated value obtained by substituting the temperature difference between Tc and Th), and the ON / OFF output from -16.4% (-16.4 V) , And the polarity is switched corresponding to the heating load, and the ON / OFF output is maintained at the cooling output + 16.4% point. From then on, linear control is applied to reach + 30%. In other words, it recognizes the condition of EMF generation and responds to ON / OFF and polarity switching instead of linear output in a certain output range.

Although the preferred embodiments of the present invention have been described, the present invention is not limited to the specific embodiments described above. It will be apparent to those skilled in the art that numerous modifications and variations can be made in the present invention without departing from the spirit or scope of the appended claims. And equivalents should also be considered to be within the scope of the present invention.

100. Main controller 200. Power supply module
300. Polarity conversion module 500. Thermoelectric module
600. Heat exchanger 700. Heat sink
610. Temperature sensor 710. Temperature sensor

Claims (3)

A main controller 100 for applying a control signal for determining whether a power source is supplied or not, to adjust a temperature of a target object to a predetermined temperature;
A power supply module 200 for converting the voltage of the AC power source to DC, adjusting the magnitude of the voltage according to the control signal applied from the main controller 100, and outputting the adjusted voltage;
A polarity switching module 300 for switching the polarity of a voltage output from the power supply module 200 according to a control signal of the main controller 100 to a positive or negative polarity and outputting the polarity; And
A heat exchanger 600 connected to the target object on one side and a heat dissipating device 700 on the other side and having a plurality of thermoelectric elements is connected to the power supply module 200 through the polarity switching module 300 And a thermoelectric module (500) having both ends thermally or thermally reacted by a supplied power source,
The main controller 100 calculates a value of an electromotive force generated in accordance with a driving condition of the thermoelectric module 500 within a predetermined constant output range in the vicinity of a polarity change point, (ON) / OFF (OFF) method, and controls to output in a linear manner in other ranges,
The main controller 100 calculates a temperature difference Δ (Th-Tc) between the temperature values received from the temperature sensors 610 and 710 installed in the heat exchanging apparatus 600 and the heat dissipating apparatus 700, Wherein a value of the electromotive force is calculated by applying a value of a Seebeck coefficient (?).
delete The method according to claim 1,
The main controller 100 controls the ON / OFF control period of the linear control period or the boundary point of the output to be switched from the ON / OFF control period to the linear control period, Wherein the absolute value of the control output is applied in a range where the absolute value of the control output is not equal to or smaller than the absolute value of the calculated electromotive force.

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