MOTOR DRIVE DEVICE AND METHOD FOR ITS CONTROL

Abstract

A motor drive device and a method for controlling it are provided to improve the torque control accuracy of an induction motor driven by an indirect vector control method. The motor drive device comprises an induction motor with a stator and a rotor, which rotates due to a rotating magnetic field generated in the stator, and a control unit for determining the rotor resistance based on a deviation between a reference torque and an output torque of the induction motor, as well as the temperature of the induction motor, and for controlling the power output of the induction motor based on the determined rotor resistance.

Description

BACKGROUND Technical field The present disclosure relates to a motor drive device and a method for controlling it in order to improve the torque control accuracy of an induction motor driven by an indirect vector control method. Description of the state of the art The induction motor, which generates a torque through the electromagnetic force of the induced current produced in the rotor by the rotating magnetic field of the stator, can directly control the torque by controlling the magnetic flux component current and the torque component current via a synchronous reference frame that rotates with the speed of the magnetic flux vector. The technique for directly controlling the torque of such induction motors can be called vector control, and vector control can be subdivided into direct vector control and indirect vector control according to a method for determining a magnetic flux angle. Of these two, direct vector control is a method for directly determining the magnetic flux angle by estimating the magnetic flux itself, and indirect vector control is a method for indirectly determining the magnetic flux angle by determining the slip angle velocity. In contrast to direct vector control, indirect vector control controls the motor's torque by indirectly estimating the magnetic flux angle via the slip angular velocity. Therefore, accurately determining the slip angular velocity is a crucial factor in improving the precision of the torque control. The slip angle velocity is generated because the rotor in the induction motor always rotates slowly compared to the synchronous speed of the rotating magnetic field, and can be determined from the ratio of rotor resistance to rotor inductance and the current reference on the synchronous reference frame. The facts described above as background technology serve only to provide a better understanding of the background of the present disclosure and are not to be understood as an acknowledgment that they correspond to prior art already known to the person skilled in the art. OVERVIEW Several aspects of the present disclosure relate to a motor drive device and a method for controlling it, which are capable of improving the torque control accuracy of an induction motor by estimating a value of a rotor resistance that changes in real time and performing indirect vector control. A motor drive device according to various aspects of the present disclosure comprises an induction motor with a stator and a rotor which rotates by means of a rotating magnetic field generated in the stator, as well as a control unit for determining a resistance of the rotor based on a deviation between a reference torque and an output torque of the induction motor and a temperature of the induction motor, and for controlling a power of the induction motor based on the determined resistance of the rotor. For example, the control unit can perform torque error control to allow the output torque to follow the reference torque based on the temperature of the induction motor, and can determine the resistance of the rotor based on a result of the torque error control. For example, the control unit can repeatedly perform torque error control until the deviation between the reference torque and the output torque is less than or equal to a predetermined reference error, and then re-determine the rotor resistance. For example, the control unit can perform torque error control using a control gain that is predetermined according to the temperature of the induction motor and the reference torque. The control gain can, for example, include proportional gain and integral gain with respect to the error between the reference torque and the output torque. For example, the control unit can perform torque error control by referring to a table in which the control gain is stored according to the temperature of the induction motor and the reference torque. For example, the control unit can correct a result of the torque error control by means of an anti-windup function with respect to the deviation between the reference torque and the output torque and determine the resistance of the rotor based on the corrected result of the torque error control. For example, the temperature of the induction motor could be the coil temperature of the stator. For example, the control unit can determine the slip angle velocity of the induction motor based on the resistance of the rotor and control the power of the induction motor based on the determined slip angle velocity. For example, an inverter can also be provided to drive the induction motor, whereby the control unit can convert a current of the stator into a synchronous reference frame based on the slip angle velocity and control the power of the induction motor by controlling the inverter using pulse width modulation (PWM control) based on the converted current. A method for controlling a motor drive device according to an exemplary embodiment of the present disclosure to achieve the above-described problem comprises determining a resistance of a rotor by a control unit based on a deviation between a reference torque and an output torque of an induction motor, which consists of a stator and the rotor which rotates by means of a rotating magnetic field generated in the stator, as well as a temperature of the induction motor, and controlling a power of the induction motor by the control unit based on the determined resistance of the rotor. For example, determining the resistance of the rotor may involve performing torque error control to allow the output torque to follow the reference torque based on the temperature of the induction motor by the control unit, and determining the resistance of the rotor based on a result of the torque error control. For example, determining the resistance of the rotor may involve the control unit repeatedly performing torque error control until the deviation between the reference torque and the output torque becomes less than or equal to a predetermined reference error in order to redetermine the resistance of the rotor. For example, determining the resistance of the rotor can involve the control unit performing torque error control using a control gain that is predetermined according to the temperature of the induction motor and the reference torque. For example, the control gain can include proportional gain and integral gain with respect to the deviation between the reference torque and the output torque. For example, determining the resistance of the rotor may involve performing torque error control by the controller with reference to a table in which the control gain is stored according to the temperature of the induction motor and the reference torque. For example, determining the resistance of the rotor may involve correcting a torque error control result by means of an anti-windup control with respect to the error between the reference torque and the output torque, and determining the resistance of the rotor based on the corrected torque error control result. For example, the temperature of the induction motor could be the coil temperature of the stator. For example, controlling the power of the induction motor can involve the control unit determining the slip angle velocity of the induction motor based on the resistance of the rotor and controlling the power of the induction motor based on the determined slip angle velocity. For example, controlling the power of the induction motor can involve the control unit converting a current from the stator into a synchronous reference frame based on the slip angle velocity, and controlling the power of the induction motor by controlling an inverter to drive the induction motor through pulse width modulation control based on the converted current. According to various exemplary embodiments of the present disclosure, as described above, the estimation accuracy of the magnetic flux angle during indirect vector control can be improved, and accordingly, the precision of the torque control can be improved by determining the slip angle velocity by the value of the rotor resistance, which changes in real time. Since the precision of the torque control is improved, the reference torque tracking performance can also be improved without a separate torque correction process. Furthermore, various exemplary embodiments of the present disclosure can be implemented by adding logic to an existing control unit (controller), thereby achieving the effects described above without increasing the volume and cost due to a separate hardware configuration. The effects achieved by the present disclosure are not limited to the effects mentioned above, and other effects not mentioned can be clearly understood by experts in the field of the present disclosure from the following description. BRIEF DESCRIPTION OF THE DRAWING FIGURES Fig. 1 is a view showing a configuration of a motor drive device according to an exemplary embodiment of the present disclosure. Fig. 2 is a view showing an example of an implementation of a motor drive device according to an exemplary embodiment of the present disclosure. Fig. 3 is a view illustrating a method for determining the rotor resistance according to an exemplary embodiment of the present disclosure. Fig. 4 is a flowchart illustrating a method for controlling a motor drive device according to an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION Specific structural or functional descriptions relating to exemplary embodiments of the present disclosure are presented only for the purpose of explaining the exemplary embodiments according to the present disclosure, and the exemplary embodiments according to the present disclosure may be implemented in various forms and should not be construed as being limited to the exemplary embodiments described in the present description or application. An exemplary embodiment according to the present disclosure can be subject to various modifications and take many forms, so that specific exemplary embodiments are shown in the drawings and described in detail in the present description. However, this is not intended to limit the exemplary embodiments according to the concepts of the present disclosure to a particular disclosed embodiment, but rather it should be understood that all modifications, equivalents, or replacements that fall within the scope of the ideas and techniques of the present disclosure are included. Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meanings as they are generally understood by those skilled in the field of the present disclosure. Terms as defined in a commonly used dictionary should be interpreted to have a meaning consistent with the meaning in the context of the relevant technology and should not be interpreted in an idealized or overly formal sense unless expressly defined as such herein. Exemplary embodiments disclosed in the present description are described in detail below with reference to the accompanying drawing figures, whereby identical or similar components are provided with the same reference numerals regardless of the drawing symbols and redundant descriptions of these are omitted. In the description of the following exemplary embodiments, the term "predetermined" means that a numerical value of a parameter is predetermined when the parameter is used in a process or algorithm. According to one exemplary embodiment, the numerical value of the parameter can be determined at the beginning of the process or algorithm or during a section in which the process or algorithm is executed. The suffixes “module” and “unit” for components used in the following description are assigned or used synonymously only for the sake of simplifying the specification and have no inherent meaning or function. In describing the exemplary embodiments disclosed in this specification, a detailed description is omitted to the extent that a detailed description of the associated known technology could obscure the core of the exemplary embodiments disclosed in this specification. Furthermore, the accompanying drawings serve only to facilitate understanding of the exemplary embodiments disclosed in this description, and the technical ideas disclosed in this description are not limited by the accompanying drawings and should be understood as encompassing all modifications, equivalents, and substitutions inherent in the nature and scope of protection of this disclosure. Terms containing ordinal numbers, such as "first" and "second," can be used to describe different components; however, the components are not limited by these terms. The terms are used solely to distinguish one component from another. When it is mentioned that a component is "connected" or "linked" to another component, it should be understood that it may be directly connected or linked to that other component, but that other components may also be in between. Conversely, when it is mentioned that a component is "directly connected" or "directly linked" to another component, it should be understood that no other components are in between. Singular expressions can include plural expressions unless the context clearly indicates otherwise. In the present description, terms such as "include" or "have" may be used to indicate the presence of features, numbers, steps, processes, components, parts or combinations thereof described in the description, and should be understood as not excluding the presence or addition of one or more other features, numbers, steps, processes, components, parts or combinations thereof. Furthermore, terms such as "engine control unit" (MCU) and "hybrid control unit" (HCU) can only be commonly used designations for control units that control vehicle-specific functions, and should not be understood as generic functional units. The control unit may include a communication device for communicating with other control units or sensors for controlling the functions for which it is responsible, a memory for storing operating systems or logic instructions and input / output information, and one or more processors for performing determinations, calculations, decisions, and the like that are necessary for controlling the functions for which it is responsible. The motor drive device and the method for controlling it according to an exemplary embodiment of the present disclosure can determine the rotor resistance based on the temperature of the induction motor and perform indirect vector control by means of the slip angle velocity derived therefrom, thereby improving the precision of the torque control. In the following, a configuration of a motor drive device will first be described with reference to Fig. 1, before a method for controlling the motor drive device according to an exemplary embodiment of the present disclosure is described. Fig. 1 is a simplified block diagram showing a configuration of a motor drive device according to an exemplary embodiment of the present disclosure. With reference to Fig. 1, a motor drive device according to an exemplary embodiment of the present disclosure can comprise an induction motor 100, a control unit 200, and an inverter 300. The motor drive device can be implemented by including more or fewer components than those shown in Fig. 1. The induction motor 100 can have a stator and a rotor that rotates due to a rotating magnetic field generated in the stator. The stator can include a coil for generating the rotating magnetic field, and the rotor can rotate due to an electromagnetic force from a current induced by the rotating magnetic field. The control unit 200 can control the power of the induction motor 100, and in particular, the control unit 200 can determine the rotor resistance based on the deviation between the reference torque and the output torque of the induction motor 100 and the temperature of the induction motor 100. Furthermore, based on the determined rotor resistance, the control unit 200 can determine the slip angle of the induction motor 100 and control the motor 100's power output based on this determined slip angle. The inverter 300 can drive the induction motor 100, for example, by switching a switching element such as an insulated-gate bipolar transistor (IGBT) and a metal-oxide-semiconductor field-effect transistor (MOSFET). Such a switching operation can be controlled by the control unit 200, and the control unit 200 can control the power of the induction motor 100 by controlling the inverter 300 based on the reference torque. Specific details regarding the motor drive device according to an exemplary embodiment of the present disclosure are described in more detail below with reference to Fig. 2 and Fig. 3. Fig. 2 is a simplified block diagram showing an example of an implementation of a motor drive device according to an exemplary embodiment of the present disclosure, and Fig. 3 is a flowchart illustrating a method for determining the rotor resistance according to an exemplary embodiment of the present disclosure. First, with reference to Fig. 2, the induction motor 100 can be configured as a three-phase motor according to an exemplary embodiment of the present disclosure, and the inverter 300 can be configured as a pulse-width modulation inverter (PWM inverter). Furthermore, the control unit 200 can comprise a magnetic flux controller 201, a current reference map 202, a current controller 203, a first transducer 204, a torque error controller 205, a first gain table 206, a second gain angle table 207, a slip angle velocity determination unit 208, a rotation angle velocity determination unit 209, a magnetic flux angle determination unit 210, and a second transducer 211. The magnetic flux controller 201 can receive a DC voltage (Vdc) and a synchronous speed (ωe) of the rotating magnetic field input to the inverter 300 and output an inverse magnetic flux (λ-1). The current reference map 202 can receive the output inverse magnetic flux (λ-1) and a reference torque (Te*) as inputs and output the corresponding d-axis current reference (ids*) and q-axis current reference (iqs*). For example, according to an exemplary embodiment, the reference torque (Te*) can be directly input into the control unit 200 or obtained from a connected upper control unit. The current controller 203 can output a d-axis voltage reference (Vds*) and a q-axis voltage reference (Vqs*) of the synchronous reference frame corresponding to the d-axis current reference (ids*) and the q-axis current reference (iqs*) of the synchronous reference frame. The output d-axis voltage reference (Vds*) and the q-axis voltage reference (Vqs*) can be converted by the first converter 204 into a three-phase voltage reference (Van*, Vbn*, Vcn*) and then fed into the inverter 300. The inverter 300 can output a voltage corresponding to the three-phase voltage reference (Van*, Vbn*, Vcn*) such that three-phase currents (ias, ibs, ics) flow in the stator of the induction motor 100 to generate the rotating magnetic field. For example, the rotor of the induction motor 100 can rotate due to an electromagnetic force caused by the induced current of the rotating magnetic field, thereby generating a torque (Te). Meanwhile, according to an exemplary embodiment of the present disclosure, the control unit 200 can comprise a torque error control unit 205 for performing torque error control, and the torque error control unit 205 can determine the rotor resistance (Rr) of the induction motor 100 based on the deviation between the reference torque (Te*) and the output torque (Te) of the induction motor 100 and the temperature (x) of the induction motor 100. More precisely, the torque error controller 205 can perform the torque error control in such a way that the output torque (Te) of the induction motor 100 can follow the reference torque (Te*) based on the temperature (x) of the induction motor 100, and can determine the resistance (Rr) of the rotor based on the result of the torque error control. For this purpose, the torque error controller 205 can have the reference torque (Te*), the output torque (Te) and the temperature (x) of the induction motor 100 as input values ​​and the resistance (Rr) of the rotor as output values. Here, the reference torque (Te*) can be entered directly into the torque error controller 205 or transferred from a higher-level controller, and the output torque (Te) can be the measured torque output by the induction motor 100, and can be measured by a sensor inside or outside the induction motor 100 to be entered into the torque error controller 205. The temperature (x) of the induction motor 100 can, for example, refer to the temperature of the stator winding of the induction motor 100 and can be measured via a temperature sensor connected to the stator winding for transmission to the torque error controller 205. However, the temperature (x) of the induction motor 100 is not necessarily limited to the temperature of the stator winding, but can also include the temperature of any location outside or inside the induction motor 100, the temperature of a rotor, and the like, and can be determined by various temperature determination / estimation methods, in addition to measurement and determination by a temperature sensor. The torque error controller 205 can perform torque error control via feedback control to adjust the output torque (Te) to the reference torque (Te*) based on the input values. Torque error control can be repeated until the error between the reference torque (Te*) and the output torque (Te) becomes less than or equal to a predetermined reference error (e.g., "0"). The rotor resistance (Rr) can be determined in real time from the result of each torque error control cycle and can be recalculated and updated in real time as the torque error control cycle is repeated. Torque error control can be implemented, for example, using proportional-integral control (PI control). In this case, the temperature (x) of the induction motor 100 can be used to determine the control gain. More precisely, the control gain of the torque error control can be predetermined according to the temperature (x) of the induction motor and the reference torque (Te*) and can be obtained, for example, from tables 206, 207, in which the control gain is stored according to each temperature (x) of the induction motor and each reference torque (Te*). Furthermore, such control gains can include a proportional gain (KP) and an integral gain (Ki) of the reference torque (Te*) and the output torque (Te), and the proportional gain (KP) and the integral gain (Ki) can be obtained from the respective gain tables 206, 207. Meanwhile, the resistance (Rr) of the rotor can be determined from the result of the torque error control, for which a relationship between the torque of the induction motor 100 and the rotor resistance (Rr), such as a voltage-torque characteristic, can be used. The following describes in more detail a process carried out by the torque error control 205 with reference to Fig. 3. With reference to Fig. 3, a block diagram of the torque error control 205 is shown, and a torque error control process carried out by the torque error control 205 is shown. First, the torque error controller 205 can subtract the output torque (Te) from the reference torque (Te*) (S310) and determine the error between the reference torque (Te*) and the output torque (Te). The torque error controller 205 can then perform a proportional-integral control by applying a value obtained by applying the proportional gain (Kp) to the error between the determined reference torque (Te*) and the output torque (Te) and a value obtained by applying the integral gain (Ki) to the error between the reference torque (Te*) and the output torque (Te) and by integrating this error (S320). For example, a value output as a result of proportional-integral control can be limited by a threshold value to prevent an accumulation of error integral values ​​(S330). For example, the torque error controller 205 can prevent deviation divergence at the time of integration by applying an anti-windup gain (Ka) to the value obtained by subtracting the threshold value from the value output as a result of proportional-integral control (S340), and then subtracting this from the error between the reference torque (Te*) and the output torque (Te) to perform the integral control (S350). By determining the resistance (Rr) of the rotor based on the temperature of the induction motor 100 in this way, indirect vector control can be carried out by taking into account the change in the resistance (Rr) of the rotor according to the temperature. Referring again to Fig. 2, the slip angular velocity determination unit 208, when the rotor resistance (Rr) is determined in the torque error control unit 205, can determine the slip angular velocity (ωsl) based on the rotor resistance (Rr) determined in the torque error control unit 205, the d-axis current reference value (ids*), the q-axis current reference value (iqs*) of the synchronous reference frame generated in the current reference map 202, and the rotor inductance (Lr). For example, a predetermined value for the rotor inductance (Lr), determined by, for example, a vehicle test or the like, can be used. More precisely, the slip angular velocity determination unit 208 can determine the slip angular velocity using the following equation. Here, the slip angle velocity (ωsl) can be determined based on the rotor resistance (Rr), which is determined by reproducing the temperature of the induction motor 100 in the torque error controller 205 in such a way that it can be determined relatively accurately by reproducing the value of the current rotor resistance (Rr). Meanwhile, the angular velocity determination unit 209 can determine the angular velocity (ωr) of the rotor of the induction motor 100 based on the detection values, and, for example, the angular velocity (ωr) of the rotor can be determined by the position of the rotor obtained by a position sensor such as a resolver. The slip angular velocity (ωsl) and angular velocity (ωr) determined in the slip angular velocity determination unit 208 and the rotation angular velocity determination unit 209 can be added to obtain the synchronous angular velocity (ωe) of the rotating magnetic field, and the magnetic flux angle determination unit 210 can determine the magnetic flux angle (θe) by integrating the synchronous angular velocity (ωe). The magnetic flux angle (θe) determined in this way can be used to convert the three-phase stator currents (ias, ibs, ics) of the induction motor 100 into the d-axis current (ids) and the q-axis current (iqs) of the synchronous reference frame in the second converter 211. For example, the second converter 211 can receive the three-phase stator current (ias, ibs, ics) as input via a current sensor connected to the stator. Afterwards, the current controller can receive 203 feedback on the converted d-axis current (ids) and the q-axis current (iqs) and perform the current control so that the d-axis current (ids) and the q-axis current (iqs) can follow the d-axis current reference value (ids*) and the q-axis current reference (iqs*). More precisely, the current controller 203 can generate a d-axis voltage reference (Vds*) and a q-axis voltage reference (Vqs*) so that the d-axis current (ids) and the q-axis current (iqs) can follow the d-axis current reference (ids*) and the q-axis current reference (iqs*) through the feedback of the converted d-axis current (ids) and the q-axis current (iqs). The generated d-axis voltage reference (Vds*) and the q-axis voltage reference (Vqs*) can be converted by the first converter 204 into three-phase voltage references (Van*, Vbn*, Vcn*), and the inverter 300 can output an AC voltage to the stator of the induction motor 300 by means of pulse width modulation control based on the three-phase voltage references (Van*, Vbn*, Vcn*) to drive the induction motor 300. In an exemplary embodiment of the present disclosure, the slip angle velocity (ωsl) can be determined by reflecting the change in rotor resistance (Rr) according to temperature changes, and accordingly, the magnetic flux angle (θe) can be determined for controlling the power of the induction motor 100 such that a relatively accurate magnetic flux angle (θe) can be obtained without the need for a separate magnetic sensor or the like for determining the magnetic flux angle (θe). In particular, a more accurate magnetic flux angle (θe) can be obtained by taking into account the change in rotor resistance (Rr) according to the temperature of the induction motor 100, instead of using a fixed value as the value of the rotor resistance (Rr) on the basis of which the power of the induction motor 100 can be controlled, thereby improving the accuracy of the torque control. The following describes a method for controlling the motor drive device according to an exemplary embodiment of the present disclosure with reference to Fig. 4. Fig. 4 is a flowchart illustrating a method for controlling a motor drive device according to an exemplary embodiment of the present disclosure. Referring to Fig. 4, a torque reference value can first be applied which enables the induction motor 100 to output a reference torque (S410), wherein this torque reference value can be determined by a required torque and can be applied directly to the control unit 200 or transmitted from a higher-level control unit connected to the control unit 200. After the torque reference value has been applied, the control unit 200 can determine whether the induction motor 100 is operating in indirect vector control mode, i.e., whether the power of the induction motor 100 is controlled by indirectly determining the magnetic flux angle via the slip angle velocity, without directly sensing the magnetic flux angle of the rotating magnetic field via a magnetic sensor or the like (S420). If the induction motor 100 is not operating in indirect vector control mode (No in S420), the subsequent control may not be performed, as there is no need to determine the slip angle velocity. If, on the other hand, the induction motor 100 is operated in indirect vector control mode (Yes in S420), the control unit 200 can detect the temperature of the induction motor 100 required to determine the slip angle velocity (S430), whereby the temperature of the induction motor 100 refers to the temperature of the stator winding and is detected via a temperature sensor connected to the stator winding. Subsequently, the control unit 200 can determine a control gain for torque error control based on the determined temperature of the induction motor 100 and the reference torque (S440). For example, the control unit 200 can determine the control gain according to the current reference torque and the temperature of the induction motor 100 by referring to the table in which the control gain is stored according to the respective reference torque and temperature of the induction motor 100, where the control gain includes a proportional gain and an integral gain. Once the control gain is determined, the control unit 200 can perform torque error control to make the output torque follow the reference torque based on the reference torque of the induction motor 100, the output torque and the control gain (S450), and can determine the value of the rotor resistance based on the result of the torque error control (S460). Once the rotor resistance is determined, the control unit 200 can determine the slip angular velocity based on the rotor resistance (S470), and the torque error control can be repeated to recalculate the value of the rotor resistance if the deviation between the reference torque and the output torque exceeds a predetermined reference error (e.g., "0") (No in S480). If, after this, the error between the reference torque and the output torque becomes less than or equal to a predetermined reference error (e.g., "0") according to the torque error control (Yes in S480), the torque error control can be terminated and the value of the rotor resistance can be maintained according to the result of the current torque error control. According to various exemplary embodiments of the present disclosure, as described above, the estimation accuracy of the magnetic flux angle during indirect vector control can be improved, and accordingly, the precision of the torque control can be improved by determining the slip angle velocity by the value of the rotor resistance, which changes in real time. Since the accuracy of the torque control is improved, the reference torque tracking performance can also be improved without a separate torque correction process. Furthermore, various exemplary embodiments of the present disclosure can be implemented by adding logic to an existing control unit in such a way that the effects described above can be achieved without increasing the volume and cost due to a separate hardware configuration. Although the present disclosure has been presented and described with reference to a particular exemplary embodiment as described above, it is obvious to those skilled in the art that the present disclosure can be improved and modified in various ways without deviating from the technical ideas of the present disclosure as set forth in the following claims.

Claims

Motor drive device, the device comprising: an induction motor with a stator and a rotor which rotates by means of a rotating magnetic field generated in the stator; and a control unit which is configured to determine a resistance of the rotor on the basis of a deviation between a reference torque and an output torque of the induction motor and a temperature of the induction motor, and which is configured to control a power of the induction motor on the basis of the determined resistance of the rotor. Device according to claim 1, wherein the control unit is configured to perform a torque error control to allow the output torque to follow the reference torque based on the temperature of the induction motor, and is configured to determine the resistance of the rotor based on a result of the torque error control. Device according to claim 2, wherein the control unit is configured to repeatedly perform the torque error control until the deviation between the reference torque and the output torque is less than or equal to a predetermined reference error, and wherein the control unit is configured to redetermine the resistance of the rotor when the output torque is less than or equal to the predetermined reference error. Device according to claim 2, wherein the control unit is configured to perform the torque error control by means of a control gain which is predetermined to correspond to the temperature of the induction motor and the reference torque. Device according to claim 4, wherein the control amplification with respect to the deviation between the reference torque and the output torque comprises a proportional amplification and an integral amplification. Device according to claim 4, wherein the control unit is configured to perform the torque error control by applying a control gain from a table containing stored control gain values ​​corresponding to the temperature of the induction motor and the reference torque. Device according to claim 2, wherein the control unit is configured to correct a result of the torque error control by means of an anti-windup control with respect to the deviation between the reference torque and the output torque, and is configured to determine the resistance of the rotor on the basis of the corrected result of the torque error control. Device according to claim 1, wherein the temperature of the induction motor is a coil temperature of the stator. Device according to claim 1, wherein the control unit is configured to determine the slip angle velocity of the induction motor based on the resistance of the rotor, and is configured to control the power of the induction motor based on the determined slip angle velocity. Device according to claim 9, further comprising: an inverter configured to drive the induction motor, wherein the control unit is configured to convert a current of the stator into a synchronous reference frame on the basis of the slip angle velocity, and is configured to control the power of the induction motor on the basis of the converted current by controlling the inverter by means of pulse width modulation control (PWM control). Method for controlling a motor drive device, the method comprising: determining a resistance of a rotor by a control unit based on a deviation between a reference torque and an output torque of an induction motor comprising a stator and the rotor rotating by means of a rotating magnetic field generated in the stator, as well as a temperature of the induction motor; and controlling a power of the induction motor by the control unit based on the determined resistance of the rotor. The method of claim 11, wherein determining the resistance of the rotor comprises performing a torque error control to allow the output torque to follow the reference torque based on the temperature of the induction motor by the control unit, and determining the resistance of the rotor based on a result of the torque error control. The method of claim 12, wherein determining the resistance of the rotor comprises repeatedly performing the torque error control by the control unit until the deviation between the reference torque and the output torque is less than or equal to a predetermined reference error, and wherein, in response to the fact that the output torque is less than or equal to the predetermined reference error, the resistance of the rotor is determined again. Method according to claim 12, wherein determining the resistance of the rotor comprises performing the torque error control by the control unit using a control gain that is predetermined according to the temperature of the induction motor and the reference torque. Method according to claim 14, wherein the control amplification with respect to the deviation between the reference torque and the output torque comprises a proportional amplification and an integral amplification. Method according to claim 14, wherein determining the resistance of the rotor comprises performing the torque error control by the control unit by applying a control gain from a table which stores the control gain according to each temperature of the induction motor and the reference torque. The method of claim 12, wherein determining the resistance of the rotor comprises correcting a result of the torque error control by means of an anti-windup control with respect to the deviation between the reference torque and the output torque, and determining the resistance of the rotor based on the corrected result of the torque error control. Method according to claim 11, wherein the temperature of the induction motor is a coil temperature of the stator. Method according to claim 11, wherein controlling the power of the induction motor comprises determining the slip angle velocity of the induction motor by the control unit based on the resistance of the rotor and controlling the power of the induction motor based on the determined slip angle velocity. Method according to claim 19, wherein controlling the power of the induction motor comprises converting a current of the stator into a synchronous reference frame by the control unit on the basis of the slip angle velocity and controlling the power of the induction motor by controlling an inverter to drive the induction motor by pulse width modulation control on the basis of the converted current.

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