FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
& THE PATENTS RULES, 2003
COMPLETE SPECIFICATION [See section 10, Rule 13]
PROTECTION DEVICE AND SERVER MOTOR;
MITSUBISHI ELECTRIC
CORPORATION, A CORPORATION ORGANISED AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3, MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 100-8310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

DESCRIPTION
Field
[0001] The present invention relates to a protection device that protects a motor, and a servomotor.
Background
[0002] A motor can excessively increase in temperature depending on usage conditions. A protection device protects the motor from damage due to such excessive temperature increase.
[0003] Patent Literature 1 discloses a concentrated-winding rotary electric machine system that monitors a temperature increase in a concentrated-winding rotary electric machine. The system includes a temperature measurement unit that measures the winding temperature on the basis of the winding current and the voltage in each phase of a stator in the concentrated-winding rotary electric machine, and a temperature increase estimation unit that estimates an increase in the winding temperature from each phase current and each voltage when the concentrated-winding rotary electric machine is in a loaded condition and in a rotation-stop state. [0004] Further, Patent Literature 2 discloses a synchronous electric motor including a current sensor that detects the AC current in two or more of three phases in the synchronous electric motor, a temperature sensor that detects the temperature of the synchronous electric motor, and a temperature protection unit that suppresses a temperature increase in the synchronous electric motor.

Citation List Patent Literatures
[0005] Patent Literature 1: Japanese Patent Application Laid-open No. 2005-80450
Patent Literature 2: Japanese Patent Application Laid-open No. 2001-268989
Summary Technical Problem
[0006] However, in Patent Literatures 1 and 2, there are variations in temperature among respective phase coils during or after DC control. When a temperature of a coil other than a coil having its temperature detected by a temperature sensor becomes high, the motor may not be protected.
[0007] The present invention has been achieved to solve the above problem, and an object of the present invention is to provide a protection device that can protect a motor even when the temperature of the coil other than the coil having its temperature detected by a temperature sensor becomes high.
Solution to Problem
[0008] To solve the problem and achieve the object, the present invention provides a protection device to protect a motor that is driven by an inverter device, the protection device comprising: a temperature detector to detect a temperature of a first-phase coil of the motor; a first resistance calculation unit to calculate a resistance of the first-phase coil on a basis of the temperature detected by the temperature detector; a current detector to detect a current to be supplied from the inverter device to the motor; and a processing unit to calculate a temperature of

a second-phase coil of the motor and a temperature of a third-phase coil of the motor, on a basis of the resistance calculated by the first resistance calculation unit and the current detected by the current detection unit, and, upon detecting that the temperature of the first-phase coil, the temperature of t.he second-phase coil, or the temperature of the third-phase coil exceeds a set temperature, output a signal to stop the motor.
Advantageous Effects of Invention
[0009] The protection device of the present invention can protect the motor even when the temperature of the coil other than the coil having its temperature detected by the "temperature sensor becomes high.
Brief Description of Drawings
[0010] FIG. 1 is a configuration diagram of a servomotor according to a first embodiment.
FIG. 2 is a flowchart for explaining an operation of a processing unit according to the first embodiment.
FIG. 3 is a configuration diagram of a servomotor according to a second embodiment.
FIG. 4 is a flowchart for explaining an operation of a processing unit according to the second embodiment.
FIG. 5 is a configuration diagram of a servomotor according to a third embodiment.
FIG. 6 is a configuration diagram of a servomotor according to a fourth embodiment.
FIG. 7 is a flowchart for explaining an operation of a processing unit according to the fourth embodiment.
FIG. 8 is a diagram illustrating a configuration example of hardware for realizing a protection device according to the first embodiment, a protection device

according to the second embodiment, a protection device according to the third embodiment, and a protection device according to the fourth embodiment.
Description of Embodiments
[0011] Exemplary embodiments of a protection device and a servomotor according to the present invention will be explained below in detail with reference to the drawings. The present invention is not limited to the embodiments. [0012] First embodiment.
FIG. 1 is a diagram illustrating the configuration of a servomotor 100 that includes a protection device 1 according to a first embodiment. FIG. 2 is a flowchart for explaining the operation of a processing unit 14 according to the first embodiment.
[0013] The servomotor 100 includes an inverter device 2, a motor 3, the protection device 1, a heat detector 4, and a rotation detector 5. The inverter device 2 converts an AC voltage supplied from an AC power supply to a DC voltage, converts again this DC voltage back to an AC voltage, and outputs the AC voltage resulting from the conversion. The motor 3 is driven by the inverter device 2. The protection device 1 protects the motor 3. The heat detector 4 is a temperature sensor that detects heat in a single-phase coil of the motor 3. The rotation detector 5 detects a rotational angle of the motor 3.
[0014] The motor 3 is constituted by a first-phase coil, a second-phase coil, and a third-phase coil. The first-phase coil is hereinafter referred to as a "U-phase coil". The second-phase coil is hereinafter referred to as a "V-phase coil". The third-phase coil is hereinafter referred to as a "W-phase coil". [0015] Although the heat detector 4 is described as

detecting heat in the U-phase coil, the heat detector 4 may detect heat in the V-phase coil or the W-phase coil. The rotation detector 5 detects the rotational angle of the motor 3.
[0016] The protection device 1 is a device that protects the motor 3 that is driven by the inverter device 2. The protection device 1 includes a temperature detection unit 11, a resistance calculation unit 12, a current detection unit 13, a processing unit 14, and a phase detection unit 15. The temperature detection unit 11 detects the temperature of the U-phase coil. The resistance calculation unit 12 is a first resistance calculation unit that calculates a resistance of the U-phase coil. The current detection unit 13 detects a current. The processing unit 14 outputs a signal to stop the motor 3. The phase detection unit 15 detects a voltage and a current phase of the motor 3 on the basis of a value detected by the rotation detector 5.
[0017] The temperature detection unit 11 detects a temperature of the U-phase coil of the motor 3 on the basis of a value detected by the heat detector 4. [0018] The resistance calculation unit 12 calculates a resistance of the U-phase coil on the basis of the temperature detected by the temperature detection unit 11. [0019] The current detection unit 13 detects a current to be supplied from the inverter device 2 to the motor 3. Specifically, the current detection unit 13 detects a current through the U-phase coil, a current through the V-phase coil, and a current through the W-phase coil. [0020] The processing unit 14 calculates a temperature of the V-phase coil of the motor 3 and a temperature of the W-phase coil of the motor 3 on the basis of the resistance calculated by the first resistance calculation unit 12, and

the current detected by the current detection unit 13. Upon detecting that the temperature of the U-phase coil, the temperature of the V-phase coil, or the temperature of the W-phase coil exceeds a set temperature, the processing unit 14 outputs the signal to stop the motor 3. [0021] A description is made below as to the specific configuration of the processing unit 14 when the motor 3 is servo-locked. Servo-lock is designed to control the operation of the motor 3 by a DC current, and hereinafter is also referred to as "DC control". When the DC control is executed, the operation of the motor 3 is stopped while a DC current is supplied from the inverter device 2 to the motor 3.
[0022] The processing unit 14 includes a voltage calculation unit 16, a resistance calculation unit 17, a temperature calculation unit 18, a signal generation unit 19, and an output unit 20. The voltage calculation unit 16 calculates a voltage of each phase coil. The resistance calculation unit 17 is a second resistance calculation unit that calculates resistances of the V-phase coil and the W-phase coil. The temperature calculation unit 18 calculates temperatures of the V-phase coil and the W-phase coil. The signal generation unit 19 generates a signal. The output unit 20 outputs the signal.
[0023] The voltage calculation unit 16 calculates the voltage of the U-phase coil, the voltage of the V-phase coil, and the voltage of the W-phase coil, on the basis of the resistance of the U-phase coil, the current detected by the current detection unit 13, and the rotational angle. The voltage calculation unit 16 may be configured by a first voltage calculation unit 16a that calculates the voltage of the U-phase coil, and a second voltage calculation unit 16b that calculates the voltage of the V-

phase coil and the W-phase coil.
[0024] The first voltage calculation unit 16a calculates the voltage of the U-phase coil on the basis of the resistance of the U-phase coil calculated by the resistance calculation unit 12, and the current through the U-phase coil detected by the current detection unit 13.
[0025] The second voltage calculation unit 16b calculates a phase voltage on the basis of the voltage of the U-phase coil., and the rotational angle. The second voltage calculation unit 16b calculates the voltage of the V-phase coil on the basis of the phase voltage and the angle obtained by adding 120 degrees to the rotational angle. The second voltage calculation unit 16b also calculates the voltage of the W-phase coil on the basis of the phase voltage and the angle obtained by adding 240 degrees to the rotatLonal angle.
[0026] The resistance calculation unit 17 calculates the resistance of the V-phase coil on the basis of the current through and the voltage of the V-phase coil, and also calculates the resistance of the W-phase coil on the basis of the current through and the voltage of the W-phase coil. [0027] The temperature calculation unit 18 calculates the temperature of the V-phase coil on the basis of the resistance of the V-phase coil, and also calculates the temperature of the W-phase coil on the basis of the resistance of the W-phase coil.
[0028] Upon detecting that the temperature of the U-phase coil, the temperature of the V-phase coil, or the temperature of the W-phase coil exceeds a set temperature, the signal generation unit 19 generates the signal to stop the motor 3. The output unit 20 outputs the signal to stop the motor 3. The set temperature, which is determined on the basis of the heat-resistant properties of the

insulating material of the coils used in the motor 3, varies depending on the insulation class rating. For class F, the heat-resistant temperature is 155 degrees. For class H, the heat-resistant temperature is 180 degrees. The value of the set temperature is obtained by subtracting "atmospheric-temperature upper-limit value + temperature tolerance" from the corresponding value of the heat-resistant temperature.
[0029] Next, the specific operation of the processing unit 14 described above is described with reference to a flowchart illustrated in FIG. 2.
[0030] At Step ST1, the protection device 1 determines whether DC control is being executed on the motor 3. When the protection device 1 determines that the DC control is being executed (YES), the process advances to Step ST2. When the protection device 1 determines that the DC control is not being executed, i.e., the motor 3 is being driven (NO), then, the process advances to Step ST13. Each of Steps ST13 to ST17 is described in a • fourth embodiment described below.
[0031] At Step ST2, the temperature detection unit 11 detects a temperature Tu of the U-phase coil. [0032] At Step ST3, the resistance calculation unit 12 calculates a resistance Ru of the U-phase coil on the basis of the temperature Tu of the U-phase coil detected at Step ST2. Specifically, the resistance calculation unit 12 calculates the U-phase resistance Ru by substituting the temperature Tu of the U-phase coil into an equation (1). "R" represents the resistance in the case of 20 degrees, and the value of "R" is already known.
Ru=(234.5+TU-20)-(234.5+20)xR • • • (1) [0033] At Step ST4, the current detection unit 13 detects a current Iu through the U-phase coil, a current Iv

through the V-phase coil, and a current Iw through the W-phase coil.
[0034] At Step ST5, the voltage calculation unit 16 calculates a voltage Eu of the U-phase coil. The voltage Eu of the U-phase coil is an instantaneous voltage. Specifically, the voltage calculation unit 16 calculates the voltage Eu of the U-phase coil by substituting the resistance Ru of the U-phase coil, and the current Iu through the U-phase coil into an equation (2).
Eu=IuxRu • • • (2) [0035] At Step ST6, the voltage calculation unit 16 calculates a voltage Ev of the V-phase coil, and a voltage Ew of the W-phase coil. Each of the voltage Ev of the V-phase coil and the voltage Ew of the W-phase coil is an instantaneous voltage. Specifically, the voltage calculation unit 16 calculates a phase voltage E by substituting the voltage Eu of the U-phase coil and a rotational angle a into an equation (3). The voltage calculation unit 16 calculates the voltage Ev of the V-phase coil by substituting the phase voltage E and the rotational angle a into an equation (4). Formula (a+2/3x7r) in the equation (4) indicates that there is a phase difference of 120 degrees between the U-phase coil and the V-phase coil. The voltage calculation unit 16 calculates the voltage Ew of the W-phase coil by substituting the phase voltage E and the rotational angle a. into an equation (5) . Formula (a+4/3x7i) in the equation (5) indicates that there is a phase difference of 240 degrees between the U-phase coil and the W-phase coil.
Eu=Excos(a) • • • (3)
Ev=Excos (a+2/3x7i) • • • (4)
Ew=Excos (a+4/3xTT) • • • (5)

[0036] For the angle of 90 degrees in the U-phase coil, the V-phase coil, and the W-phase coil, the calculation is difficult. When the rotational angle a is 90 degrees, thus, the rotational angle a may be substituted by 91 degrees to thereby obtain an approximate value.
[0037] Although a voltage detector directly detects the voltage of each phase coil, it is thought that during the DC control, the detected voltage may be so low as to cause a significant error. Therefore, at Steps ST5 and ST6, the voltage of each phase coil is calculated by the voltage calculation unit 16.
[0038] At Step ST7, the resistance calculation unit 17 calculates a resistance Rv of the V-phase coil, and a resistance Rw of the W-phase coil. Specifically, the resistance calculation unit 17 calculates the resistance Rv of the V-phase coil by substituting into an equation (6) the voltage Ev of and the current Iv through the V-phase coil. The resistance calculation unit 17 calculates the resistance Rw of the W-phase coil by substituting into an equation (7) the voltage Ew of and the current Iw through the W-phase coil.
Rv=Ev-rIv • • • (6) RW=EWTIW • • • (7) [0039] At Step ST8, the temperature calculation unit 18 calculates a temperature Tvl of the V-phase coil, and a temperature Twl of the W-phase coil. Specifically, the temperature calculation unit 18 calculates the temperature Tvl of the V-phase coil by substituting into an equation (8) the resistance Rv of the V-phase coil, calculated at Step ST7, and the resistance R in the case of 20 degrees. The temperature calculation unit 18 calculates the temperature Twl of the W-phase coil by substituting into an equation (9) the resistance Rw of the W-phase coil,

calculated at Step ST7, and the resistance R in the case of 20 degrees.
Rv=(234.5+Tvl-20)+(234.5+20)xR • • • (8)
Rw=(234.5+Twl-20)+(234.5+2 0)xR • • • (9) [0040] At Step ST9, the signal generation unit 19 determines whether the temperature Tul of the U-phase coil, the temperature Tvl of the V-phase coil, or the temperature Twl of the W-phase coil exceeds a set temperature. When the signal generation unit 19 determines that any one of the coil temperatures exceeds the set temperature (YES), the process advances to Step ST11. When the signal generation unit 19 determines that none of the coil temperatures exceeds the set temperature (NO), the process advances to Step ST10.
[0041] At Step ST10, the temperature calculation unit 18 stores the temperature Tul of the U-phase coil, the temperature Tvl of the V-phase coil, and the temperature Twl of the W-phase coil, in a storage unit 21. When the process advances to Step ST10 from Step ST17 described later, the temperature calculation unit 18 stores a temperature Tu2 as the temperature Tul, a temperature Tv2 as the temperature Tvl, and a temperature Tw2 as the temperature Twl in the storage unit 21. At the time of cold start, nTul=Tvl=Twl=0" is set. After performing Step ST10, the process returns to Step ST1.
[0042] At Step ST11, the signal generation unit 19 generates a signal to stop the motor 3.
[0043] At Step ST12, the output unit 20 outputs the signal to stop the motor 3, to the inverter device 2. When the signal to stop the motor 3 is input to the inverter device 2, the inverter device 2 stops supply of the DC current to the motor 3. Since the supply of the DC current to the motor 3 is stopped, the motor 3 is cooled, and its

temperature is decreased.
[0044] Therefore, in a state where DC control is executed on the motor 3, the protection device 1 outputs the signal to stop driving the motor 3 when any of the coil temperatures exceeds the set temperature. Accordingly, even when the temperature of the coil other than the coil having its temperature detected by the heat detector 4 becomes high, the protection device 1 can still protect the motor 3.
[0045] Further, the protection device 1 calculates the temperature of each phase coil in real time by directly using the instantaneous voltage and current values. Therefore, even when the cooling state of the motor 3 changes, the protection device 1 can still calculate the temperature of each phase coil in response to the change in cooling state.
[0046] The motor 3 provides a determined driving pattern as the driving of the motor 3 and the DC control on the motor 3 are repeatedly performed. The temperature of each phase coil varies depending on the phase of the electrical angle because the temperature increase during the DC control is determined by the DC current. The protection device 1 calculates the temperature of each phase coil in real time during the DC control and, when any one of the coil temperatures exceeds the set temperature, stops driving the motor 3, such that the protection device 1 can protect the motor 3. [0047] Second embodiment.
Next, a description is made below as to the configuration of a servomotor 101 that includes a protection device 6 according to a second embodiment. FIG. 3 is a diagram illustrating the configuration of the servomotor 101 according to the second embodiment. FIG. 4

is a flowchart for explaining the operation of a processing unit 31 according to the second embodiment.
[0048] The servomotor 101 includes the inverter device 2, the motor 3, the protection device 6, the heat detector 4, and the rotation detector 5. The inverter device 2 converts an AC voltage supplied from an AC power supply to a DC voltage, converts again this DC voltage back to an AC voltage, and outputs the AC voltage resulting from the conversion. The motor 3 is driven by the inverter device 2. The protection device 6 protects the motor 3. The heat detector 4 detects heat in a single-phase coil of the motor 3. The rotation detector 5 detects a rotational angle of the motor 3.
[0049] The motor 3 is constituted by a first-phase coil, a second-phase coil, and a third-phase coil. The first-phase coil is hereinafter referred to as a "U-phase coil". The second-phase coil is hereinafter referred to as a "V-phase coil". The third-phase coil is hereinafter referred to as a "W-phase coil".
[0050] Although the heat detector 4 is described as detecting heat in the U-phase coil, the heat detector 4 may detect heat in the V-phase coil or the W-phase coil. The rotation detector 5 detects the rotational angle of the motor 3.
[0051] The servomotor 101 according to the second embodiment has a configuration identical to the servomotor 100 according to the first embodiment, except that the protection device 6 is different in configuration from the protection device 1. Hereinafter, like constituent elements as those of the servomotor 100 are denoted by like reference signs.
[0052] The configuration and the operation of the protection device 6 are described below. The protection

device 6 is a device that protects the motor 3 that is driven by the inverter device 2. The protection device 6 includes the temperature detection unit 11, the resistance calculation unit' 12', the current detection unit 13, a processing unit 31, and the phase detection unit 15. The temperature detection unit 11 detects the temperature of the U-phase coil. The resistance calculation unit 12 is a first resistance calculation unit that calculates the resistance of the U-phase coil. The current detection unit 13 detects the current. The processing unit 31 outputs a signal to stop the motor 3. The phase detection unit 15 detects the voltage and the current phase of the motor 3. [0053] The temperature detection unit 11 detects the temperature of the U-phase coil on the basis of the value detected by the heat detector 4.
[0054] The resistance calculation unit 12 calculates the resistance of the U-phase coil on the basis of the temperature detected by the temperature detection unit 11. [0055] The current detection unit 13 calculates a current through the W-phase coil on the basis of a detected current through the U-phase coil or a detected current through the V-phase coil, and the rotational angle. Specifically, the current detection unit 13 includes a detection unit 13a that detects the current of the U-phase coil and the current of the V-phase coil, and a calculation unit 13b that calculates the current of the W-phase coil. [0056] A description is made below as to the specific configuration of the processing unit 31 in a state where the DC control is executed on the motor 3.
[0057] The processing unit 31 includes the storage unit 21, a resistance calculation unit 32, a copper-loss calculation unit 33, a temperature calculation unit 34, the signal generation unit 19, and the output unit 20. The

storage unit 21 stores therein a temperature of the V-phase coil and a temperature of the W-phase coil. The resistance calculation unit 32 is a second resistance calculation unit that calculates a resistance of the V-phase coil and a resistance of the W-phase coil. The copper-loss calculation unit 33 calculates a copper loss. The temperature calculation unit 34 calculates the temperature of the V-phase coil, and the temperature of the W-phase coil. The signal generation unit 19 generates a signal. The output unit 20 outputs the signal. [0058] The storage unit 21 stores therein the temperature of the V-phase coil, and the temperature of the W-phase coil, which have been calculated by the previous processing.
[0059] The resistance calculation unit 32 calculates the resistance of the V-phase coil on the basis of the temperature of the V-phase coil stored in the storage unit 21. The resistance calculation unit 32 calculates the resistance of the W-phase coil on the basis of the temperature of the W-phase coil stored in the storage unit 21.
[0060] The copper-loss calculation unit 33 calculates the copper loss in the U-phase coil on the basis of the current through and the resistance of the U-phase coil, calculates the copper loss in the V-phase coil on the basis of the current through and the resistance of the V-phase coil, and calculates the copper loss in the W-phase coil on the basis of the current through and the resistance of the W-phase coil.
[0061] The temperature calculation unit 34 calculates the thermal resistance on the basis of the copper loss in and the temperature of the U-phase coil. The temperature calculation unit 34 calculates the temperature of the V-

phase coil on the basis of the calculated thermal resistance and the copper loss in the V-phase coil, and also calculates the temperature of the W-phase coil on the basis of the calculated thermal resistance and the copper loss in the W-phase coil. Specifically, the temperature calculation unit 34 includes a time measuring'unit 34a, a thermal-resistance calculation unit 34b, and a calculation unit 34c. The time measuring unit 34a measures time. The thermal-resistange calculation unit 34b calculates the thermal resistance. The calculation unit 34c calculates the temperature of the V-phase coil and the temperature of the W-phase coil. In the thermal-resistance calculation unit 34b, the time measuring unit 34a measures a time tl at which DC control is started, and also measures a time t2 at which n-seconds has elapsed since the start of the DC control. The thermal-resistance calculation unit 34b calculates the thermal resistance on the basis of a temperature of the U-phase coil at the time tl, a temperature of the U-phase coil at the time t2, and the copper loss in the'U-phase coil.
[0062] Upon detecting that the temperature of the U-phase coil, the temperature of the V-phase coil, or the temperature of the W-phase coil exceeds a set temperature, the signal generation unit 19 generates a signal to stop driving the motor 3. The output unit 20 outputs the signal to stop the motor 3.
[0063] Next, the specific operation of the processing unit 31 described above is described with reference to a flowchart illustrated in FIG. 4. It is assumed that the storage unit 21 has stored therein the temperature Tvl of the V-phase coil, and the temperature Twl of the W-phase coil, which have been calculated by the previous processing. [0064] At Step ST21, the protection device 6 determines

whether the DC control is being executed on the motor 3. When the protection device 6 determines that the DC control is being executed (YES), the process advances to Step ST22. When the protection device 6 determines that the DC control is not being executed, i.e., the motor 3 is being driven (NO), then, the process advances to Step ST13. Each of Steps ST13 to ST17 is described in the fourth embodiment described below.
[0065] At Step ST22, the temperature detection unit 11 detects a temperature Tu of the U-phase coil. [0066] At Step ST23, the resistance calculation unit 12 calculates a resistance Ru of the U-phase coil on the basis of the temperature Tu of the U-phase coil detected at Step ST22. Specifically, the resistance calculation unit 12 calculates the resistance Ru of the U-phase coil by substituting the temperature Tu of the U-phase coil into an equation (10). "R" represents the resistance in the case of 20 degrees, and the value of "R" is a constant.
Ru=(234.5+TU-20)-(234.5+20)xR • • - (10) [0067] At Step ST24, the resistance calculation unit 32 calculates a resistance Rv of the V-phase coil, and a resistance Rw of the W-phase coil. Specifically, the resistance calculation unit 32 reads the temperature Tvl of the V-phase coil, and the temperature Twl of the W-phase coil both of which are stored in the storage unit 21. Then, the resistance calculation unit 32 substitutes the temperature Tvl of the V-phase coil into an equation (11) to calculate the resistance Rv of the V-phase coil, and, also, substitutes the temperature Twl of the W-phase coil into an equation (12) to calculate the resistance Rw of the W-phase coil.
Rv=(234.5+Tvl-20)-(234.5+2 0)xR • • • (11)

RW=(234.5+TW1-2 0)H-(234.5+2 0)XR • • • (12) [0068] At Step ST25, the current detection unit 13 calculates a current Iw through the W-phase coil. The specific operation of the current detection unit 13 is described below. A current Iu through the U-phase coil, and a current Iv through the V-phase coil are directly detected by the current detection unit 13.
[0069] The current detection unit 13 calculates a phase
current I by substituting the current Iu through the U-
phase coil into an equation (13). The current detection
unit 13 may calculate the phase current I by substituting
the current Iv through the V-phase coil into an equation
(14). The current detection unit 13 calculates the current
Iw through the W-phase coil by substituting the phase
current I and the rotational angle a. into an equation (15) .
Iu^Ixcos(a) • • • (13)
Iv-Ixcos (a+2/3x7T) • • • (14) Iw=Ixcos (a+4/3x7i) • • • (15) [0070] - At Step ST26, the copper-loss calculation unit 33 calculates a copper loss Pu in the U-phase coil, a copper loss Pv in the V-phase coil, and a copper loss Pw in the W-phase coil. Specifically, the copper-loss calculation unit 33 calculates the copper loss Pu in the U-phase coil by substituting into an equation (16) the current Iu through and the resistance Ru of the U-phase coil. The copper-loss calculation unit 33 calculates the copper loss Pv in the V-phase coil by substituting into an equation (17) the current Iv through and the resistance Rv of the V-phase coil. The copper-loss calculation unit 33 calculates the copper loss Pw in the W-phase coil by substituting into an equation (18) the current Iw through and the resistance Rw of the W-phase coil.

Pu=Iu2xRu • • • (16)
Pv=Iv2xRv • • • (17)
Pw=Iw2xRw • • • (18) [0071] At Step ST27, the temperature calculation unit 34 calculates a thermal resistance Rth on the basis of the copper loss Pu in and the temperature Tu of the U-phase coil. The thermal resistance Rth is a thermal resistance generated between the U-phase coil and the atmosphere. Specifically, when a temperature of the U-phase coil, detected at the start of the DC control, is defined as a temperature Tul, and a temperature of the U-phase coil, detected after a lapse of n-seconds since the start of the DC control, is defined as a temperature Tu2, the temperature calculation unit 34 calculates a thermal resistance Rth [K/W] by substituting the n (sec) and the copper loss Pu in the U-phase coil into an equation (19). The sign "C" represents a thermal capacity [J/K], and the value of "C" is already known. The "C" is less affected by temperature dependence. The thermal resistance Rth in the equation (19) is an exponential function, and is therefore calculated using difference calculation, Z-transform, or bilinear transform.
Tu2=(PuxRth)x(l-exp(-n^(CxRth)))+Tulxexp(-n-(CxRth))
• • -(19) [0072] At Step ST28, the temperature calculation unit 34 calculates a temperature Tv2 of the V-phase coil, and a temperature Tw2 of the W-phase coil. Specifically, the temperature calculation unit 34 calculates the temperature Tv2 of the V-phase coil by substituting into an equation (20) the thermal resistance Rth, the copper loss Pv in the V-phase coil, and the temperature Tvl of the V-phase coil stored in the storage unit 21. The temperature calculation

unit 34 calculates the temperature Tw2 of the W-phase coil by substituting into an equation (21) the thermal resistance Rth, the copper loss Pw in the W-phase coil, and the temperature Twl of the W-phase coil stored in the storage unit 21. The thermal resistance Rth is the same value for the three phases.
Tv2=(PvxRth)x(l-exp(-n^(CxRth)))+Tvlxexp(-n-(CxRth)) •••(20)
Tw2=(PwxRth)x(l-exp(-n-r (CxRth) ) ) +Twlxexp (-n-f- (CxRth) ) ' • '(21) [0073] At Step ST29, the signal generation unit 19 determines whether the temperature Tu2 of the U-phase coil, the temperature Tv2 of the V-phase coil, or the temperature Tw2 of the W-phase coil exceeds a set temperature. When the signal generation unit 19 determines that any one of the coil temperatures exceeds the set temperature (YES), the process advances to Step ST31. When the signal generation unit 19 determines that none of the coil temperatures exceeds the set temperature (NO), the process advances to Step ST30.
[0074] At Step ST30, the temperature calculation unit 34 stores the temperature Tu2 of the U-phase coil, the temperature Tv2 of the V-phase coil, and the temperature Tw2 of the W-phase coil, in the storage unit 21. The temperature calculation unit 18 stores the temperature Tu2 as the temperature Tul, the temperature Tv2 as the temperature Tvl, and the temperature Tw2 as the temperature Twl, in the storage unit 21. At the time of the cold start, "Tul=Tvl=Twl=0" is set. After performing Step ST30, the process returns to Step ST21.
[0075] At Step ST31, the signal generation unit 19 generates a signal to stop the motor 3. [0076] At Step ST32, the output unit 20 outputs the

signal to stop the motor 3, to the inverter device 2. When the signal to stop the motor 3 is input to the inverter device 2, the inverter device 2 stops supply of the DC current to the motor 3. Since the supply of the DC current to the motor 3 is stopped, the motor 3 is cooled, and its temperature is decreased.
[0077] Therefore, in the state where the DC control is executed on the motor 3, the protection device 6 outputs the signal to stop driving the motor 3 when any of the coil temperatures exceeds the set temperature. Accordingly, even when the temperature of the coil other than the coil having its temperature detected by the heat detector 4 becomes high, the protection device 6 can still protect the motor 3.
[0078] The protection device 6 sets a thermal capacity in advance, calculates the temperature of each phase coil at the set timing, and detects whether any of the coil temperatures exceeds the set temperature. Therefore, when the cooling state of the motor 3 changes, and any of the coil temperatures exceeds the set temperature, the protection device 6 stops driving the motor 3, and can thereby protect the motor 3. [007 9] Third embodiment.
Next, a description is made as to the configuration of a servomotor 102 that includes a protection device 7 according to a third embodiment. FIG. 5 is a diagram illustrating the configuration of the servomotor 102 according to the third embodiment. Although the description of the third embodiment is based on the assumption that the motor 3 is a water-cooled motor, the motor 3 is not limited to the water-cooled motor. [0080] The servomotor 102 includes the inverter device 2 the motor 3, the protection device 7, the heat detector 4,

and the rotation detector 5. The inverter device 2 converts an AC voltage supplied from an AC power supply to a DC voltage, converts again this DC voltage back to an AC voltage, and outputs the AC voltage resulting from the conversion. The motor 3 is driven by the inverter device 2. The protection device 7 protects the motor 3. The heat detector 4 detects heat in a single-phase coil of the motor 3. The rotation detector 5 detects a rotational angle of the motor 3.
[0081] The motor 3 is constituted by a first-phase coil, a second-phase coil, and a third-phase coil. The first-phase coil is hereinafter referred to as a "U-phase coil". The second-phase coil is hereinafter referred to as a "V-phase coil". The third-phase coil is hereinafter referred to as a "W-phase coil".
[0082] Although the heat detector 4 is described as detecting heat in the U-phase coil, the heat detector 4 may detect heat in the V-phase coil or the W-phase coil. The rotation detector 5 detects the rotational angle of the motor 3.
[0083] The protection device 7 in the servomotor 102 according to the third embodiment has a configuration identical to the protection device 6 in the servomotor 101 according to the second embodiment, except that a processing unit 41 is different in configuration from the processing unit 31. Hereinafter, like constituent elements as those in the servomotor 101 are denoted below by like reference signs.
[0084] A description is made below as to a specific configuration of the processing unit 41 in a state where the DC control is executed on the motor 3. [0085] The processing unit 41 includes the copper-loss calculation unit 33, the time measuring unit 34a, the

thermal-resistance calculation unit 34b, the signal generation unit 19, and the output unit 20. The copper-loss calculation unit 33 calculates a copper loss. The time measuring unit 34a measures time. The thermal-resistance calculation unit 34b calculates a thermal resistance. The signal generation unit 19 generates a signal. The output unit 20 outputs the signal. [0086] The copper-loss calculation unit 33 calculates the copper loss in the U-phase coil on the basis of the current through and the resistance of the U-phase coil. Specifically, the copper-loss calculation unit 33 calculates the copper loss Pu in the U-phase coil by substituting into an equation (22) the current Iu through and the resistance Ru of the U-phase coil.
Pu=Iu2xRu • • • (22) [0087] The thermal-resistance calculation unit 34b calculates the thermal resistance on the basis of the copper loss in and the temperature of the U-phase coil. Specifically, in the thermal-resistance calculation unit 34b, the time measuring unit 34a measures the time tl at which the DC control is started, and also measures the time t2 at which n-seconds have elapsed since the start of DC control. When the temperature of the U-phase coil detected at the time tl is defined as a temperature Tul, and the temperature of the U-phase coil detected at the time t2 is defined as a temperature Tu2, the thermal-resistance calculation unit 34b calculates a thermal resistance Rth [K/W] by substituting the copper loss Pu in the U-phase coil into an equation (23). The sign "C" represents a thermal capacity [J/K], and the value of "C" is already known. The thermal resistance Rth in the equation (23) is an exponential function, and is therefore calculated using difference calculation, Z-transform, or bilinear transform.

Tu2-(PuxRth)x (l-exp(-n4-(CxRth) ) )+Tulxexp (-n^ (CxRth) ) • ' '(23) [0088] Upon detecting that the thermal resistance calculated by the thermal-resistance calculation unit 34b exceeds a set resistance, the signal generation unit 19 generates a signal to stop driving the motor 3. The output unit 20 outputs the signal to stop the motor 3. [0089] Therefore, in the state where the DC control is executed on the motor 3, the protection device 7 outputs the signal to stop driving the motor 3 when the thermal resistance exceeds the set resistance. Accordingly, even when the temperature of the coil other than the coil having its temperature detected by the heat detector 4 becomes high, the protection device 7 can still protect the motor 3. [0090] The protection device 7 sets a thermal capacity in advance, calculates the thermal resistance at the set timing, and detects whether the calculated thermal resistance exceeds the set resistance. Therefore, when the cooling state of the motor 3 changes, and the calculated thermal resistance exceeds the set resistance, then the protection device 7 stops driving the motor 3, and can thereby protect the motor 3. [00 91] Fourth embodiment.
Next, a description is made below as to the configuration of a servomotor 103 that includes a protection device 8 according to a fourth embodiment. FIG. 6 is a diagram illustrating the configuration of the servomotor 103 according to the fourth embodiment. FIG. 7 is a flowchart for explaining the operation of a processing unit 52 according to the fourth embodiment.
[0092] The servomotor 103 includes the inverter device 2 the motor 3, the protection device 8, the heat detector 4, and the rotation detector 5. The inverter device 2

converts an AC voltage supplied from an AC power supply to a DC voltage, converts again this DC voltage back to an AC voltage, and outputs the AC voltage resulting from the conversion. The motor 3 is driven by the inverter device 2. The protection device-8 protects the motor 3. The heat detector 4 detects heat in a single-phase coil of the motor 3. The rotation detector 5 detects a rotational angle of the motor 3.
[0093] The motor 3 is constituted by a first-phase coil, a second-phase coil, and a third-phase coil. The first-phase coil is hereinafter referred to as a "U-phase coil". The second-phase coil is hereinafter referred to as a "V-phase coil". The third-phase coil is hereinafter referred to as a "W-phase coil".
[0094] Although the heat detector 4 is described as detecting heat in the U-phase coil, the heat detector 4 may detect heat in the V-phase coil or the W-phase coil. The rotation detector 5 detects the rotational angle of the motor 3.
[0095] The protection device 8 in the servomotor 103 -according to the fourth embodiment has a configuration identical to the protection device 6 in the servomotor 101 according to the second embodiment, except that the processing unit 52 is different in configuration from the processing unit 31. Hereinafter, like constituent elements as those in the servomotor 101 are denoted below by like reference signs.
[0096] The protection device 8 includes the temperature detection unit 11, the current detection unit 13, a voltage detection unit 51, the processing unit 52, and the phase detection unit 15. The temperature detection unit 11 detects the temperature of the U-phase coil. The current detection unit 13 detects the current. The voltage

detection unit 51 detects a voltage to be supplied from the inverter device 2 to the motor 3. The processing unit 52 outputs a signal to stop the motor 3. The phase detection unit 15 detects the voltage and the current phase of the motor 3 on the basis of the value detected by the rotation detector 5.
[0097] A description is made below as to a specific configuration of the processing unit 52 in a state where the motor 3 is driven. The processing unit 52 includes the storage unit 21, a torque-value calculation unit 53, a rotational-speed detection unit 54, an output calculation unit 55, an input calculation unit 56, a total-loss calculation unit 57, a temperature calculation unit 58, the signal generation unit 19, and the signal generation unit 19. The storage unit 21 stores therein a temperature of the V-phase coil and a temperature of the W-phase coil. The torque-value calculation unit 53 calculates a torque value. The rotational-speed detection unit 54 detects a rotational speed of the motor 3. The output calculation unit 55 calculates an output. The input calculation unit 56 calculates an input. The total-loss calculation unit 57 calculates a total loss. The temperature calculation unit 58 calculates a temperature of the V-phase coil and a temperature of the W-phase coil. The signal generation unit 19 generates a signal. The output unit 20 outputs the signal.
[0098] The storage unit 21 stores therein the temperature of the V-phase coil, and the temperature of the W-phase coil, which have been calculated by the previous processing.
[0099] The torque-value calculation unit 53 calculates the torque value on the basis of the current detected by the current detection unit 13. Specifically, the torque-

value calculation unit 53 calculates the torque value by performing dq-coordinate transformation on the basis of the current detected by the current detection unit 13. [0100] The rotational-speed detection unit 54 substitutes the number of poles of the motor 3, and a frequency f detected by the inverter device 2 into an equation (24) to detect a rotational speed N of the motor 3.
N=120-^fx (number of poles in motor) •••(24) [0101] The output calculation unit 55 calculates the output on the basis of the torque value and the rotational speed of the motor 3. Specifically, the output calculation unit 55 calculates an output Pout by substituting a torque value T and the rotational speed N into an equation (25).
Pout=Tx (2TIXN-60) -1000 • • • (25) [0102] The input calculation unit 56 calculates the input on the basis of the current detected by the current detection unit 13, and the voltage detected by the voltage detection unit 51. Specifically, the input calculation unit 56 calculates an input Pin by substituting a current I and a voltage V into an equation (26) . The sign "cos(3" represents a power factor.
Pin=V3xIxV*cosp • • • (26)
[0103] The total-loss calculation unit 57 calculates the total loss caused by driving the motor 3, on the basis of the output and the input. Specifically, the total-loss calculation unit 57 calculates a total loss P by subtracting the output Pout from the input Pin as expressed by an equation (27).
P=Pin-Pout •••(27)
[0104] The temperature calculation unit 58 calculates the thermal resistance on the basis of the total loss and the temperature of the U-phase coil. The temperature

calculation unit 58 calculates the temperature of the V-phase coil and the temperature of the*W-phase coil on the basis of the calculated thermal resistance and the total loss. Specifically, the temperature calculation unit 58 includes a time measuring unit 58a, a thermal-resistance calculation unit 58b, and a calculation unit 58c. The time measuring unit 58a measures time. The thermal-resistance calculation unit 58b calculates the thermal resistance. The calculation unit 58c calculates the temperature of the V-phase coil and the temperature of the W-phase coil. In the thermal-resistance calculation unit 58b, the time measuring unit 58a measures the time tl at which driving of the motor 3 is started, and also measures the time t2 at which the driving of the motor 3 is finished. The thermal-resistance calculation unit 58b calculates the thermal resistance on the basis of the temperature of the U-phase coil at the time tl, the temperature of the U-phase coil at the time t2, and the total loss.
[0105] Upon detecting that the temperature of the U-phase coil, the temperature of the V-phase coil, or the temperature of the W-phase coil exceeds a set temperature, the signal generation unit 19 generates a signal to stop driving the motor 3. The output unit 20 outputs the signal to stop the motor 3.
[0106] Next, the specific operation of the processing unit 52 described above is described with reference to a flowchart illustrated in FIG. 7. The description below is made as to the operation of the processing unit 52 when, at Steps ST1 and ST21 described above, it is determined that the DC control is not being executed on the motor 3 (NO), i.e., the motor 3 is being driven.
[0107] At Step ST13, in the temperature calculation unit 58, the time measuring unit 58a measures the set driving

time.
[0108] At Step ST14, the temperature calculation unit 58 calculates the time from the start of the driving to the end of driving the motor 3 on the basis of the measured driving time. The time calculated by the temperature calculation unit 58 is hereinafter referred to as "nl". [0109] At Step ST15, the temperature calculation unit 58 calculates the thermal resistance Rth on the basis of the total loss P calculated by the total-loss calculation unit 57, and the temperature Tu of the U-phase coil detected by the temperature detection unit 11. Specifically, when the temperature of the U-phase coil, detected by the temperature detection unit 11 at the start of driving the motor 3 is defined as a temperature Tul, and the temperature of the U-phase coil, detected by the temperature detection unit 11 at the end of driving the motor 3 is defined as a temperature Tu2, the temperature calculation unit 58 calculates a thermal resistance Rth [K/W] by substituting into an equation (28) the total loss P and the time nl calculated at Step ST14. The sign "C" represents a thermal capacity [J/K], and the value of "C" is already known. The thermal resistance Rth in the equation (28) is an exponential function, and is therefore calculated using difference calculation, Z-transform, or bilinear transform.
Tu2=(PxRth)x(l-exp(-nl-r(CxRth) ) ) +Tulxexp (-nl^- (CxRth) )
••'(28) [0110] At Step ST16, the temperature calculation unit 58 calculates a temperature Tv2 of the V-phase coil, and a temperature Tw2 of the W-phase coil. Specifically, the temperature calculation unit 58 calculates the temperature Tv2 of the V-phase coil by substituting into an equation (29) the thermal resistance Rth, the total loss P, and the

temperature Tvl of the V-phase coil stored in the storage unit 21. The temperature calculation unit 58 also calculates the temperature Tw2 of the W-phase coil by substituting into an equation (30) the thermal resistance Rth, the total loss P, and the temperature Twl of the W-phase coil stored in the storage unit 21. The thermal resistance Rth is the same value for the three phases while the total loss P is the same value for the three phases. At the time of the cold start, "Tul=Tvl=Twl" is set.
Tv2=(PxRth)x (l-exp(-nl-MCxRth) ) ) +Tvlxexp (-nl-^ (CxRth) ) • • -(29)
Tw2= (PxRth) x (1-exp (-nl-f (CxRth) ) ) +Twlxexp (-nl- (CxRth) ) ••-(30) [0111] At Step ST17, the signal generation unit 1.9 determines whether the temperature Tu2 of the U-phase coil, the temperature Tv2 of the V-phase coil, or the temperature Tw2 of the W-phase coil exceeds a set temperature. When the signal generation unit 19 determines that any one of the coil temperatures exceeds the set temperature (YES), the process advances to Step ST11 or Step ST31. When the signal generation unit 19 determines that none of the coil temperatures exceeds the set temperature (NO), the process advances to Step ST10 or Step ST30.
[0112] Therefore, in the state where the motor 3 is driven, the protection device 8 outputs the signal to stop driving the motor 3 when any of the coil temperatures exceeds the set temperature. Accordingly, even when the temperature of the coil other than the coil having its temperature is detected by the heat detector 4 becomes high, the protection device 8 can still protect the motor 3. [0113] In a state where the driving of the motor 3 and the DC control on the motor 3 are repeated in a short time, and the temperature of each phase coil differs, the

protection device 8 stops driving the motor 3 when any of . the coil temperatures exceeds the set temperature, such that the protection device 8 can protect the motor 3. [0114] Each of the protection device 1 according to the first embodiment, the protection device 6 according to the second embodiment, the protection device 7 according to the third embodiment, and the protection device 8 according to the fourth embodiment may be configured by a CPU 201 that performs computation, a ROM 202 that stores therein a program read by the CPU 201, a RAM 203 that is used to run the program stored in the ROM 202, and an interface 204 that receives and outputs a signal, as illustrated in FIG. 8.
[0115] Specifically, the ROM 202 stores therein a program that implements the functions of the respective constituent elements of the protection device 1 described above. The CPU 201 reads the program stored in the ROM 202 into the RAM 203, and calculates the voltage of the U-phase coil, the voltage of the V-phase coil, and the voltage of the W-phase coil, on the basis of the resistance of and the current through the U-phase coil, and the rotational angle. The CPU 201 calculates the resistance of the V-phase coil on the basis of the current through and the voltage of the V-phase coil, and also calculates the resistance of the W-phase coil on the basis of the current through and the voltage of the W-phase coil. The CPU 201 calculates the temperature of the V-phase coil on the basis of the resistance of the V-phase coil, and also calculates the temperature of the W-phase coil on the basis of the resistance of the W-phase coil. Upon detecting that the temperature of the U-phase coil, the temperature of the V-phase coil, or the temperature of the W-phase coil exceeds the set temperature, the CPU 201 generates the signal to

stop driving the motor 3. The signal to stop driving the motor 3 is output to the inverter device 2 via the interface 204.
[0116] The ROM 202 stores therein a program that implements the functions of the respective constituent elements of the protection device 6 described above. The CPU 201 reads the program stored in the ROM 202 into the RAM 203, calculates the resistance of the V-phase coil on the basis of the temperature of the V-phase coil, and calculates the resistance of the W-phase coil on the basis of the temperature of the W-phase coil. The CPU 201 calculates the copper loss in the U-phase coil on the basis of the current through and the resistance of the U-phase coil, calculates the copper loss in the V-phase coil on the basis of the current through and the resistance of the V-phase coil, and calculates the copper loss in the W-phase coil on the basis of the current through and the resistance of the W-phase coil. The CPU 201 calculates the thermal resistance on the basis of the copper loss in and the temperature of the U-phase coil, calculates the temperature of the V-phase coil on the basis of the calculated thermal resistance and the copper loss in the V-phase coil, and calculates the temperature of the W-phase coil on the basis of the calculated thermal resistance and the copper loss in the W-phase coil. Upon detecting that the temperature of the U-phase coil, the temperature of the V-phase coil, or the temperature of the W-phase coil exceeds the set temperature, the CPU 201 generates the signal to stop driving the motor 3. The signal to stop driving the motor 3 is output to the inverter device 2 via the interface 204. [0117] The ROM 202 stores therein a program that implements the functions of the respective constituent elements of the protection device 7 described above. The

CPU 201 reads the program stored in the ROM 202 into the RAM 203, and calculates the copper loss in the U-phase coil on the basis of the current through and the resistance of the U-phase coil. The CPU 201 calculates the thermal resistance on the basis of the copper loss in and the temperature of the U-phase coil. Upon detecting that the calculated thermal resistance exceeds the set resistance, the CPU 201 generates the signal to stop driving the motor 3. The signal to stop driving the motor 3 is output to the inverter device 2 via the interface 204. [0118] The ROM 202 stores therein a program that implements the functions of the respective constituent elements of the protection device 8 described above. The CPU 201 reads the program stored in the ROM 202 into the RAM 203, and calculates the torque value on the basis of the current. The CPU 201 detects the rotational speed of the motor 3. The CPU 201 calculates the output on the basis of the torque value and the rotational speed of the motor 3. The CPU 201 calculates the input on the basis of the detected current and voltage. The CPU 201 calculates the total loss caused by driving the motor 3, on the basis of the output and the input. The CPU 201 calculates the thermal resistance on the basis of the total loss and the temperature of the U-phase coil, and calculates the temperature of the V-phase coil and the temperature of the W-phase coil on the basis of the calculated thermal resistance and the total loss. Upon detecting that the temperature of the U-phase coil, the temperature of the V-phase coil, or the temperature of the W-phase coil exceeds the set temperature, the CPU 201 generates the signal to stop driving the motor 3. The signal to stop driving the motor 3 is output to the inverter device 2 via the interface 204.

[0119] The configurations described in the above' embodiments are only an example of the contents of the present invention. The configurations can be combined with other well-known techniques, and a part of each configuration can be omitted or modified without departing from the scope of the present invention.
Reference Signs List *■
[0120] 1, 6, 7, 8 protection device, 2 inverter device, 3 motor, 4 heat detector, 5 rotation detector, 11 temperature detection unit, 12, 32, 34 resistance calculation unit, 13 current detection unit, 13a detection unit, 13b calculation unit, 14, 31, 41, 52 processing unit, 15 phase detection unit, 16 voltage calculation unit, 16a first voltage calculation unit, 16b second voltage calculation unit, 17 resistance calculation unit, 18, 34, 58 temperature calculation unit, 19 signal generation unit, 20 output unit, 21 storage unit, 33 copper-loss calculation unit, 34a, 58a time measuring unit, 34b, 58b thermal-resistance calculation unit, 34c, 58c calculation unit, 53 torque-value calculation unit, 54 rotational-speed detection unit, 55 output calculation unit, 56 input calculation unit, 57 total-loss calculation unit, 100, 101, 102, 103 servomotor.

We Claim :
1. A protection device to protect a motor that is driven by an inverter device, the protection device comprising:
a temperature detection unit to detect a temperature of a first-phase coil of the motor;
a first resistance calculation unit to calculate a resistance of the first-phase coil on a basis of the temperature detected by the temperature detection unit;
a current detection unit to detect a current to be supplied from the inverter device to the motor; and
a processing unit to calculate a temperature of a second-phase coil of the motor and a temperature of a third-phase coil of the motor, on a. basis of the resistance calculated by the first resistance calculation unit and the current detected by the current detection unit, and, upon detecting that the temperature of the first-phase coil, the temperature of the second-phase coil, or the temperature of the third-phase coil exceeds a set temperature, output a signal to stop the motor.
2. The protection device according to claim 1, wherein
in a state where DC control is executed on the motor, the protection device comprises an angle detection unit to detect a rotational angle of the motor,
the current detection unit detects a current through the first-phase coil, a current through the second-phase coil, and a current through the third-phase coil, and the processing unit includes
a voltage calculation unit to calculate a voltage of the first-phase coil, a voltage of the second-phase coil, and a voltage of the third-phase coil on a basis of the resistance of the first-phase coil, the current detected by the current detection unit, and the rotational angle,

a second resistance calculation unit to calculate a resistance of the second-phase coil on a basis of the current through and the voltage of the second-phase coil, and calculate a resistance of the third-phase coil on a basis of the current through and the voltage of the third-phase coil,
a temperature calculation unit to calculate the temperature of the second-phase coil on a basis of the resistance of the second-phase coil, and calculate the temperature of the third-phase coil on a basis of the resistance of the third-phase coil,
a signal generation unit to generate the signal to stop the motor upon detecting that the temperature of the first-phase coil, the temperature of the second-phase coil, or the temperature of the third-phase coil exceeds the set temperature, and
an output unit to output the signal.
3. The protection device according to claim 1, wherein
in a state where DC control is executed on the motor, the protection device comprises an angle detection unit to detect a rotational angle of the motor,
the current detection unit calculates a current through the third-phase coil on a basis of a detected current through the first-phase coil or a detected current through the second-phase coil, and the rotational angle, and
the processing unit includes
a storage unit to store therein a temperature of the second-phase coil, and a temperature of the third-phase coil, which have been calculated by previous processing, a second resistance calculation unit to calculate a resistance of the second-phase coil on a basis of the

temperature of the second-phase coil, and calculate a resistance of the third-phase coil on a basis of the temperature of the third-phase coil,
a copper-loss calculation unit to calculate a copper loss in the first-phase coil on a basis of the current through and the resistance of the first-phase coil, calculate a copper loss in the second-phase coil on a basis of the current through and the resistance of the second-phase coil, and calculate a copper loss in the third-phase coil on a basis of the current through and the resistance of the third-phase coil,
a temperature calculation unit to calculate a thermal resistance on a basis of the copper loss in and the temperature of the first-phase coil, calculate the temperature of the second-phase coil on a basis of the calculated thermal resistance and the copper loss in the second-phase coil, and calculate the temperature of the third-phase coil on a bas'is of the calculated thermal resistance and the copper loss in the third-phase coil,
a signal generation unit to generate the signal to stop the motor upon detecting that the temperature of the first-phase coil, the temperature of the second-phase coil, or the temperature of the third-phase coil exceeds the set temperature, and
an output unit to output the signal.
4. The protection device according to claim 1, wherein in a state where DC control is executed on the motor, the processing unit includes
a copper-loss calculation unit to calculate a copper loss in the first-phase coil on a basis of the current through and the resistance of the first-phase coil,
a thermal-resistance calculation unit to calculate a

thermal resistance on a basis of the copper loss in and the temperature of the first-phase coil,
a signal generation unit to generate the signal to stop the motor upon detecting that the thermal resistance exceeds a set resistance, and
an output unit to output the signal.
5. The protection device according to claim 1, wherein
in a state where the motor is driven,.
the protection device comprises:
an angle detection unit to detect a rotational angle of the motor; and
a voltage detection'unit to detect a voltage to be Supplied from the inverter device to the motor,
the current detection unit calculates a current through the third-phase coil on a basis of a detected current through the first-phase coil or a detected current through the second-phase coil, and the rotational angle, and %
the processing unit includes
a storage unit to store therein a temperature of the second-phase coil, and a temperature of the third-phase coil, which have been calculated by previous processing,
a torque-value calculation unit to calculate a torque value on a basis of the current detected by the current detection unit,
a rotational-speed detection unit to detect a rotational speed of the motor,
an output calculation unit to calculate an output on a basis of the torque value and the rotational speed of the motor,
an input calculation unit to calculate an input on a basis of the current detected by the current detection unit

and the voltage detected by the voltage detection unit,
a total-loss calculation unit to calculate a total loss caused by driving the motor, on a basis of the input and the output,
a temperature calculation unit to calculate a thermal resistance on a basis of the total loss and the temperature of the first-phase coil, and calculate the temperature of the second-phase coil and the temperature of the third-phase coil on a basis of the calculated thermal resistance and the total loss,
a signal generation unit to generate the signal to stop the motor upon detecting that the temperature of the first-phase, coil, the temperature of the second-phase coil, or the temperature of the third-phase coil exceeds the set temperature, and
an output unit to output the signal.
6. A servomotor comprising the protection device according to any one of claims 1 to 5.