Patent Publication Number: US-2022220966-A1

Title: Motor driving apparatus and air conditioner including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Korean Patent Application No. 10-2021-0002688, filed on Jan. 8, 2021, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE PRESENT DISCLOSURE 
     1. Field of the Invention 
     The present disclosure relates to a motor driving apparatus and an air conditioner including the same, and more particularly to a motor driving apparatus capable of preventing burnout of a switching device for switching connection of motor windings, and an air conditioner including the same. 
     2. Description of the Related Art 
     An air conditioner is an apparatus that discharges cool or hot air into a room in order to adjust room temperature and to purify air in the room, thereby providing a comfortable room environment to users. Generally, the air conditioner includes an indoor device installed in the room, the indoor device including a heat exchanger, and an outdoor device for supplying refrigerant to the indoor device, the outdoor device including a compressor and a heat exchanger. 
     PCT Publication No. W019-008756 (hereinafter referred to as a “prior art”) discloses a switching device for switching motor windings to Y-connection and A-connection in order to improve power conversion efficiency or a motor driving efficiency when a compressor motor of a compressor is driven. 
     However, in the prior art, a mechanical switch or an electrical switch is required as the switching device in order to switch windings of the motor to Y-connection and A-connection, and when repeatedly used, the switch may be damaged or its life may be degraded. 
     SUMMARY OF THE PRESENT DISCLOSURE 
     It is an object of the present disclosure to provide a motor driving apparatus capable of preventing burnout of a switching device for switching connection of a motor, and an air conditioner including the same. 
     It is another object of the present disclosure to provide a motor driving apparatus capable of preventing burnout of an inverter, and an air conditioner including the same. 
     It is another object of the present disclosure to provide a motor driving apparatus capable of controlling a brake chopper circuit at a DC terminal not to operate during the operation of the switching device. 
     In accordance with an aspect of the present disclosure, the above and other objects can be accomplished by providing a motor driving apparatus and an air conditioner including the same, which include: an inverter having a plurality of switching elements, and configured to output alternating current (AC) power to a motor based on a switching operation; a switching device disposed between the inverter and the motor, and configured to switch windings of the motor to a first connection or a second connection; and a controller configured to control the inverter and the switching device, wherein in response to the windings of the motor being switched from the first connection to the second connection, the controller controls an operating frequency of the motor to be less than or equal to a first frequency, and in response to the windings of the motor being switched from the second connection to the first connection, the controller controls an operating frequency of the motor to be less than or equal to a second frequency which is less than the first frequency. 
     Meanwhile, the motor driving apparatus and the air conditioner including the same according to an embodiment of the present disclosure may further include: a DC terminal capacitor configured to store a DC terminal voltage; a DC terminal voltage detector configured to detect the DC terminal voltage; and a brake chopper circuit connected to both ends of the DC terminal capacitor and having a resistor and a switching element. 
     Meanwhile, in response to the windings of the motor being switched from the first connection to the second connection, the controller may control the operating frequency of the motor to be less than or equal to the first frequency for the detected DC terminal voltage to be less than or equal to an allowable voltage. 
     Meanwhile, in response to the windings of the motor being switched from the first connection to the second connection, the controller controls an output of the inverter to be stopped, wherein after the output of the inverter is stopped, a regenerative current from the motor is supplied to the DC terminal through the switching device and the inverter, and wherein the controller controls the operating frequency of the motor to be less than or equal to the first frequency during the supply of the regenerative current for the detected DC terminal voltage to be less than or equal to the allowable voltage. 
     Meanwhile, in response to the windings of the motor being switched from the first connection to the second connection, the controller may control the operating frequency of the motor to decrease to the first frequency or less for the switching element in the brake chopper circuit not to be turned on. 
     Meanwhile, in response to the windings of the motor being switched from the first connection to the second connection, the controller may control an output of the inverter to be stopped, and may control a first regenerative current from the motor to be supplied to the DC terminal, and then a second regenerative current, which is lower than the first regenerative current, to be supplied to the DC terminal for the switching element in the brake chopper circuit not to be turned on that after the output of the inverter is stopped. 
     Meanwhile, in response to the windings of the motor being switched from the second connection to the first connection, the controller may control the operating frequency of the motor to be less than or equal to the second frequency for the detected DC terminal voltage to be less than or equal to the allowable range. 
     Meanwhile, in response to the windings of the motor being switched from the second connection to the first connection, the controller may control an output of the inverter to be stopped, and wherein after the output of the inverter is stopped, a regenerative current from the motor may be supplied to the DC terminal through the switching device and the inverter, and wherein the controller may control the operating frequency of the motor to be less than or equal to the second frequency during the supply of the regenerative current for the detected DC terminal voltage to be less than or equal to the allowable voltage. 
     Meanwhile, in response to the windings of the motor being switched from the second connection to the first connection, the controller may control the operating frequency of the motor to decrease to the second frequency or less for the switching element in the brake chopper circuit not to be turned on. 
     Meanwhile, in response to the windings of the motor being switched from the second connection to the first connection, the controller may control an output of the inverter to be stopped, and may control a third regenerative current from the motor to be supplied to the DC terminal, and then a fourth regenerative current, which is lower than the third regenerative current, to be supplied to the DC terminal for the switching element in the brake chopper circuit not to be turned on that after the output of the inverter is stopped. 
     Meanwhile, the controller may control an operating frequency range of the motor, during switching of the windings of the motor from the first connection to the second connection, to be greater than an operating frequency range of the motor during switching of the windings of the motor from the second connection to the first connection. 
     Meanwhile, in response to the windings of the motor being switched from the first connection to the second connection, the controller may control the operating frequency of the motor to be greater than or equal to a first reference frequency, and in response to the windings of the motor being switched from the second connection to the first connection, the controller may control the operating frequency of the motor to be greater than or equal to a second reference frequency. 
     Meanwhile, the motor driving apparatus and the air conditioner including the same according to an embodiment of the present disclosure may further include a temperature detector attached to the inverter and configured to detect temperature of the inverter, wherein in response to the windings of the motor being switched from the first connection to the second connection, the controller may control the temperature of the inverter to be less than or equal to the first reference temperature, and in response to the windings of the motor being switched from the second connection to the first connection, the controller may control the temperature of the inverter to be less than or equal to the second reference temperature which is higher than the first reference temperature. 
     In accordance with another aspect of the present disclosure, the above and other objects can be accomplished by providing a motor driving apparatus and an air conditioner including the same, which include: an inverter having a plurality of switching elements, and configured to output alternating current (AC) power to a motor based on a switching operation; a temperature detector attached to the inverter, and configured to detect temperature of the inverter; a switching device disposed between the inverter and the motor, and configured to switch windings of the motor to a first connection or a second connection; and a controller configured to control the inverter and the switching device, wherein in response to the windings of the motor being switched from the first connection to the second connection, the controller may control the temperature of the inverter to be less than or equal to a first reference temperature, and in response to the windings of the motor being switched from the second connection to the first connection, the controller may control the temperature of the inverter to be less than or equal to a second reference temperature which is higher than the first reference temperature. 
     Meanwhile, the motor driving apparatus and the air conditioner including the same according to an embodiment of the present disclosure may further include: a DC terminal capacitor configured to store a DC terminal voltage; a DC terminal voltage detector configured to detect the DC terminal voltage; and a brake chopper circuit connected to both ends of the DC terminal capacitor and having a resistor and a switching element, wherein in response to the windings of the motor being switched from the second connection to the first connection, the controller controls the temperature of the inverter to be less than or equal to the second reference temperature for the detected DC terminal voltage to be less than or equal to an allowable voltage. 
     Meanwhile, in response to the windings of the motor being switched from the first connection to the second connection, the controller may control an output of the inverter to be stopped, and wherein after the output of the inverter is stopped, a regenerative current from the motor may be supplied to the DC terminal through the switching device and the inverter, and wherein the controller may control the temperature of the inverter to be less than or equal to the second reference temperature during the supply of the regenerative current for the detected DC terminal voltage to be less than or equal to the allowable voltage. 
     Meanwhile, in response to the windings of the motor being switched from the first connection to the second connection, the controller may control the temperature of the inverter to decrease to the first reference temperature or less for the switching element in the brake chopper circuit not to be turned on. 
     Meanwhile, in response to the windings of the motor being switched from the first connection to the second connection, the controller may control an output of the inverter to be stopped, and may control a first regenerative current from the motor to be supplied to the DC terminal, and then a second regenerative current, which is lower than the first regenerative current, to be supplied to the DC terminal for the switching element in the brake chopper circuit not to be turned on that after the output of the inverter is stopped. 
     Meanwhile, in response to the windings of the motor being switched from the second connection to the first connection, the controller may control the temperature of the inverter to be less than or equal to the second reference temperature for the detected DC terminal voltage to be less than or equal to the allowable voltage. 
     Meanwhile, in response to the windings of the motor being switched from the second connection to the first connection, the controller may control an output of the inverter to be stopped, and wherein after the output of the inverter is stopped, a regenerative current from the motor may be supplied to the DC terminal through the switching device and the inverter, and wherein the controller may control the temperature of the inverter to be less than or equal to the second reference temperature during the supply of the regenerative current for the detected DC terminal voltage to be less than or equal to the allowable voltage. 
     Meanwhile, in response to the windings of the motor being switched from the second connection to the first connection, the controller may control the temperature of the inverter to decrease to the second reference temperature or less for the switching element in the brake chopper circuit not to be turned on. 
     Meanwhile, in response to the windings of the motor being switched from the second connection to the first connection, the controller may control an output of the inverter to be stopped, and may control a third regenerative current from the motor to be supplied to the DC terminal, and then a fourth regenerative current, which is lower than the third regenerative current, to be supplied to the DC terminal for the switching element in the brake chopper circuit not to be turned on that after the output of the inverter is stopped. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and other advantages of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a view showing the construction of an air conditioner according to an embodiment of the present disclosure; 
         FIG. 2  is a schematic view showing an outdoor device and an indoor device of  FIG. 1 ; 
         FIG. 3  is an internal block diagram schematically illustrating the air conditioner of  FIG. 1 ; 
         FIG. 4  is an internal block diagram illustrating a motor driving apparatus according to an embodiment of the present disclosure; 
         FIG. 5  is an internal circuit diagram illustrating the motor driving apparatus of  FIG. 4 ; 
         FIG. 6  is an internal block diagram illustrating an inverter controller of  FIG. 5 ; 
         FIG. 7  is a diagram referred to in the description of an operation of a switching device of  FIG. 4 ; 
         FIGS. 8A and 8B  are timing diagrams illustrating a winding switching operation of the switching device of  FIG. 7 ; 
         FIGS. 9A to 9I  are diagrams referred to in the description of a switching device of  FIG. 4 ; 
         FIG. 10  is a flowchart illustrating an operating method of a motor driving apparatus according to an embodiment of the present disclosure; 
         FIGS. 11 to 13B  are diagrams referred to in the description of the operating method of  FIG. 10 ; 
         FIG. 14  is a flowchart illustrating an operating method of a motor driving apparatus according to another embodiment of the present disclosure; 
         FIG. 15  is a flowchart illustrating an operating method of a motor driving apparatus according to another embodiment of the present disclosure; and 
         FIG. 16  is a diagram referred to in the description of the operation of  FIG. 15 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Exemplary embodiments of the present disclosure will be described with reference to the accompanying drawings. 
     The terms “module” and “unit,” when attached to the names of components are used herein to help the understanding of the components and thus they should not be considered as having specific meanings or roles. Accordingly, the terms “module” and “unit” may be used interchangeably. 
       FIG. 1  is a view showing the construction of an air conditioner according to an embodiment of the present disclosure. 
     As illustrated in  FIG. 1 , the air conditioner according to the embodiment of the present disclosure is a large-sized air conditioner  100 , and may include a plurality of indoor devices  31  to  35 , a plurality of outdoor devices  21  and  22  connected to the plurality of indoor devices  31  to  35 , a plurality of remote controls  41  to  45  connected to the respective indoor devices, and a remote controller  10  for controlling the plurality of indoor devices and outdoor devices. 
     The remote controller  10  may be connected to the plurality of indoor devices  31  to  36  and the plurality of outdoor devices  21  and  22  to monitor and control operations thereof. In this case, the remote controller  10  may be connected to the plurality of indoor devices to perform operation setting, locking setting, schedule control, group control, and the like. 
     Any one of a stand type air conditioner, a wall mount type air conditioner, and a ceiling type air conditioner may be used as the air conditioner  100 , but a ceiling type air conditioner will be described below by way of example, for the convenience of description. 
     In addition, the air conditioner may further include at least one of a ventilator, an air purifier, a humidifier, and a heater, which may be operated in response to the operations of the indoor devices and the outdoor devices. 
     The outdoor devices  21  and  22  may include a compressor (not shown) for receiving and compressing a refrigerant, an outdoor heat exchanger (not shown) for heat exchange between the refrigerant and outside air, an accumulator (not shown) for extracting a gaseous refrigerant from the received refrigerant and supplying the refrigerant to the compressor, and a four-way valve (not shown) for selecting a refrigerant passage for a heating operation. In addition, the outdoor devices  21  and  22  may further include a plurality of sensors, valves, an oil recovery unit, etc., but a description thereof will be omitted below. 
     The outdoor devices  21  and  22  operate the compressor and the outdoor heat exchanger included therein, to compress or heat exchange the refrigerant according to a setting, and supply the refrigerant to the indoor devices  31  to  35 . The outdoor devices  21  and  22  are driven by a request from the remote controller  10  or the indoor devices  31  to  35 , and a cooling/heating capacity changes according to the driven outdoor devices, such that a number of operating outdoor devices and a number of operating compressors installed in the outdoor devices may change. 
     In this case, the following description will be made based on an example in which the plurality of outdoor devices  21  and  22  respectively supply the refrigerant to each of the indoor devices connected thereto, but depending on a connection structure of the outdoor devices and the indoor devices, the plurality of outdoor devices may be connected to each other to supply the refrigerant to the plurality of indoor devices. 
     The indoor devices  31  to  35  may be connected to any one of the plurality of outdoor devices  21  and  22 , to be supplied with the refrigerant and to discharge cool or hot air into a room. The indoor devices  31  to  35  include an indoor heat exchanger (not shown), an indoor fan (not shown), an expansion valve (not shown) in which the supplied refrigerant is expanded, and a plurality of sensors (not shown). 
     In this case, the outdoor devices  21  and  22  and the indoor devices  31  to  35  may be connected to each other via a communication line to transmit and receive data therebetween, and the outdoor devices  21  and  22  and the indoor devices  31  to  35  may be connected to the remote controller  10  via another communication line to operate under the control of the remote controller  10 . 
     The remote controls  41  to  45 , which are connected to the respective indoor devices, may transmit a user&#39;s control command to the indoor devices, and may receive and display information about the state of the indoor devices. In this case, the remote controls communicate by wire or wirelessly with the indoor devices depending on the manner in which the input devices are connected to the indoor devices, and in some cases a single remote control may be connected to the plurality of indoor devices such that settings of the plurality of indoor devices may be changed by the input of the single remote control. 
     In addition, each of the remote controls  41  to  45  may include a temperature sensor provided therein. 
       FIG. 2  is a schematic view showing an outdoor device and an indoor device of  FIG. 1 . 
     Referring to the drawing, the air conditioner  100  is basically divided into an indoor device  31  and an outdoor device  21 . 
     The outdoor device  21  includes a compressor  102  for compressing refrigerant, a compressor motor  102   b  for driving the compressor, an outdoor heat exchanger  104  for cooling the compressed refrigerant, an outdoor blower  105  including an outdoor fan  105   a  disposed at one side of the outdoor heat exchanger  104  for accelerating the cooling of the refrigerant and a motor  105   b  for rotating the outdoor fan  105   a , an expansion valve  106  for expanding the condensed refrigerant, a cooling/heating switch valve  110  for changing the path of the compressed refrigerant, and an accumulator  103  for temporarily storing the gaseous refrigerant, removing moisture and foreign matter from the refrigerant, and supplying the refrigerant to the compressor under a predetermined pressure. 
     An indoor device  31  includes an indoor heat exchanger  109  disposed in a room for performing cooling/heating and an indoor heat exchanger  109  including an indoor fan  109   a  disposed at one side of the indoor heat exchanger  109  for accelerating the cooling of the refrigerant and a motor  109   b  for rotating the indoor fan  109   a.    
     At least one indoor heat exchanger  109  may be installed. An inverter compressor or a fixed speed compressor may be used as the compressor  102 . 
     In addition, the air conditioner  100  may be configured as a cooler for cooling a room or as a heat pump for cooling or heating a room. 
     A single indoor device  30   a  and a single outdoor device  20  are shown in  FIG. 2 . However, the present disclosure is not limited thereto. The present disclosure may also be applied to a multi-type air conditioner including a plurality of indoor devices and a plurality of outdoor devices or an air conditioner including a single indoor device and a plurality of outdoor devices. 
     The compressor  102  in the outdoor device  21  may be driven by a motor driving apparatus  220  for compressor driving, which drives a compressor motor  230 . 
       FIG. 3  is an internal block diagram schematically illustrating the air conditioner of  FIG. 1 . 
     Referring to the drawing, the air conditioner  100  of  FIG. 3  includes the compressor  102 , an outdoor fan  105   a , an indoor fan  109   a , a controller  170 , a discharge temperature sensor  118 , an outdoor temperature sensor  138 , an indoor temperature sensor  158 , and a memory  140 . 
     In addition, the air conditioner  100  may further include a compressor driver  220 , an outdoor fan driver  200 , an indoor fan driver  300 , a switch valve  110 , an expansion valve  106 , a display device  130 , and an input device  120 . 
     The compressor  102 , the outdoor fan  105   a , and the indoor fan  109   a  are described above with reference to  FIG. 2 . 
     The input device  120  has a plurality of operation buttons, and transmits a signal for an operating target temperature of the air conditioner  100  to the controller  170 . 
     The display device  130  may display an operating state of the air conditioner  100 . 
     The memory  140  may store data required for the operation of the air conditioner  100 . 
     The discharge temperature sensor  118  may sense refrigerant discharge temperature Tc at the compressor  102 , and may transmit a signal for the sensed refrigerant discharge temperature Tc to the controller  170 . 
     The outdoor temperature sensor  138  may sense outdoor temperature To, which is ambient temperature around the outdoor device  21  of the air conditioner  100 , and may transmit a signal for the sensed outdoor temperature To to the controller  170 . 
     The indoor temperature sensor  158  may sense indoor temperature Ti, which is ambient temperature around the indoor device  31  of the air conditioner  100 , and may transmit a signal for the sensed indoor temperature Ti to the controller  170 . 
     The controller  170  may control the air conditioner  100  to operate based on at least one of the sensed refrigerant discharge temperature Tc, the sensed outdoor temperature To, and the sensed indoor temperature Ti, and the input target temperature. For example, the controller  170  may control the air conditioner  100  to operate by calculating a final target superheat degree. 
     Further, in order to control operations of the compressor  102 , the indoor fan  109   a , and the outdoor fan  105   a , the controller  170  may control the compressor driver  220 , the outdoor fan driver  200 , and the indoor fan driver  300 , respectively, as illustrated herein. 
     For example, the controller  170  may output a corresponding speed reference signal to the compressor driver  220 , the outdoor fan driver  200 , or the indoor fan driver  300  based on the target temperature. 
     Further, based on each speed reference signal, the compressor motor (not shown), the motor  230 , the indoor fan motor  109   b  may operate at each target rotation speed. 
     The controller  170  may control the overall operation of the air conditioner  100 , in addition to the control of the compressor driver  220 , the outdoor fan driver  200 , or the indoor fan driver  300 . 
     For example, the controller  170  may control the operation of the cooling/heating switch valve  110  or a four-way valve. 
     Alternatively, the controller  170  may control the operation of expansion equipment or the expansion valve  106 . 
       FIG. 4  is an internal block diagram illustrating a motor driving apparatus according to an embodiment of the present disclosure; and  FIG. 5  is an internal circuit diagram illustrating the motor driving apparatus of  FIG. 4 . 
     Referring to the drawings, the motor driving apparatus  220  according to an embodiment of the present disclosure is used for driving a motor in a sensorless mode, and may be referred to as a power conversion device. 
     The motor driving apparatus  220  according to the embodiment of the present disclosure may include a converter  410 , a brake chopper circuit  415 , an inverter  420 , an inverter controller  430 , a switching device  450 , a DC terminal voltage detector B, a DC terminal capacitor C, an output current detector E, and an output voltage detector F. In addition, the motor diving apparatus  220  may further include an input current detector A and the like. 
     The input current detector A may detect an input current i s  input from a commercial AC power source  405 . To this end, a current transformer (CT), shunt resistor and the like may be used as the input current detector A. The detected input current i s , which is a pulse type discrete signal, may be input to the inverter controller  430 . 
     The converter  410  converts a voltage, having output from the commercial AC power source  405  and passed through the reactor L, into a DC voltage, and outputs the DC voltage. While the commercial AC power source  405  is shown as a three-phase AC power source, the commercial AC power may also be a single-phase AC power source. The internal structure of the converter  410  may change according to the type of the commercial AC power source  405 . 
     The converter  410  may include diodes without a switching element, such that the converter  410  may perform a rectification operation without performing a separate switching operation. 
     For example, six diodes may be arranged in the form of a bridge for the three-phase AC power source, and four diodes may be arranged in the form of a bridge for the single-phase AC power source. 
     The converter  410  may include six switching elements and six diodes for the three-phase AC power source, and in the case of single-phase AC power, a half-bridge type converter having two switching elements and four diodes may be used as the converter  410 . 
     When the converter  410  is provided with switching elements, the converter  410  may perform voltage boosting, power factor improvement, and DC voltage conversion according to a switching operation of the switching element. 
     The DC terminal capacitor C is disposed at the DC terminal, and stores the voltage output from the converter  410 . In the drawing, a single device is exemplified as the dc terminal capacitor C, but a plurality of devices may be provided to ensure device stability. 
     Further, while it is illustrated that the DC terminal capacitor C is connected to the output terminal of the converter  410 , the present disclosure is not limited thereto, and a DC voltage may be directly input to the DC terminal capacitor C. 
     For example, a DC voltage from a solar cell may be directly input to the DC terminal capacitor C or may be DC/DC converted and then input to the DC terminal capacitor C. The following description will be based on parts illustrated in the figure. 
     Both terminals n 1 -n 2  of the DC terminal capacitor may be referred to as DC terminals or DC link terminals since DC voltage is stored in the DC terminal capacitor. 
     The dc terminal voltage detector B may detect a voltage Vdc applied between both terminals of the DC terminal capacitor C. To this end, the DC terminal voltage detector B may include a resistor, an amplifier, and the like. The detected DC terminal voltage Vdc, which is a pulse type discrete signal, may be input to the controller  430 . 
     The brake chopper circuit  415  is disposed at both ends of the dc terminal capacitor C, and may include a resistor Rp and switching elements Sp. 
     Specifically, a diode element Dp and the resistor element Rp are connected in parallel to each other at one end n 1  of the do terminal capacitor C, and the switching element Sp is connected to the other end n 2  of the dc terminal capacitor C. 
     A cathode terminal of the diode element Dp is connected to the one end n 1  of the dc terminal capacitor C, and an anode terminal of the diode element Dp is connected to a terminal n 3  between the resistor element Rp and the switching element Sp. 
     If a dc terminal voltage Vdc exceeds an allowable voltage, the brake chopper circuit  415  operates, and if a dc terminal voltage Vdc is less than or equal to the allowable voltage, the brake chopper circuit  415  does not operate. 
     Specifically, if the dc terminal voltage Vdc exceeds the allowable voltage, the switching element Sp of the brake chopper circuit  415  is turned on, such that a current flows through the resistor element Rp and the switching element Sp, and thus the dc terminal voltage Vdc decreases. 
     By contrast, if the dc terminal voltage Vdc is less than or equal to the allowable voltage, the switching element Sp of the brake chopper circuit  415  is turned off, such that no current flows through the resistor element Rp and the switching element Sp. 
     By the operation of the brake chopper circuit  415 , it is possible to prevent the dc terminal voltage from rapidly rising due to a regenerative current, thereby preventing burnout of the dc terminal capacitor C and the like. 
     Particularly, the burnout of the dc terminal capacitor C and the like may be prevented when the dc terminal capacitor C is implemented as a film capacitor. 
     The inverter  420  may include a plurality of inverter switching elements Sa˜Sc and S′a˜S′c, and may convert the DC voltage Vdc at the DC terminal into three-phase AC voltages Va, Vb, and Vc according to on/off operations of the switching element Sa˜Sc and S′a˜S′c and output the voltages to the three-phase synchronous motor  250 . 
     In the inverter  420 , the upper arm switching element Sa, Sb, Sc and the lower arm switching element S′a, S′b, and S′c which are connected in series with each other form a pair, and a total of three pairs of upper and lower arm switching elements are connected in parallel with each other Sa&amp;S′a, Sb&amp;S′b, and Sc&amp;S′c. Diodes are connected in reverse parallel to each of the switching elements Sa, S′a, Sb, S′b, Sc, and S′c. 
     The switching elements in the inverter  420  are turned on/off based on the inverter switching control signal Sic from the inverter controller  430 . Thus, the three-phase AC voltages of predetermined frequencies are output to the three-phase synchronous motor  230 . 
     The temperature detector DT is attached to the inverter  420  to detect temperature of the inverter  420 . The detected temperature may be transmitted to the inverter controller  430 . 
     The inverter controller  430  may control the switching operation of the inverter  420  in a sensorless mode. To this end, the inverter controller  430  may receive an output current io detected by the output current detector E. 
     In order to control the switching operation of the inverter  420 , the inverter controller  430  may output an inverter switching control signal Sic to the inverter  420 . The inverter switching control signal Sic is a pulse width modulation (PWM)-based switching control signal, and is generated based on the output current io detected by the output current detector E and the generated signal is output. An operation of outputting the inverter switching control signal Sic in the inverter controller  430  will be descried in detail later with reference to  FIG. 6 . 
     The output current detector E detects the output current io flowing between the inverter  420  and the three-phase motor  230 . That is, the output current detector E detects a current flowing through the motor  230 . The output current detector E may detect all three phase output currents ia, ib, and ic, or may detect two phase output currents using three phase equilibrium. 
     The output current detector E may be disposed between the inverter  420  and the motor  230 , and may use a current transformer (CT), a shunt resistor, and so on for current detection. 
     When the shunt resistor is used, three shunt resistors may be disposed between the inverter  420  and the synchronous motor  230 , or one end thereof may be connected to the respective three lower arm switching element S′a, S′b, and S′c of the inverter  420 . 
     Further, two shunt resistors may also be used based on three phase equilibrium. In the case where one shunt resistor is used, the shunt resistor may be disposed between the capacitor C and the inverter  420 . 
     The detected output current io, which is a pulse type discrete signal, may be applied to the inverter controller  430 , and the inverter switching control signal Sic may be generated based on the detected output current io. In the following description, the detected output current io may correspond to three-phase output currents ia, ib, and ic. 
     The output voltage detector F may detect an output voltage vo output from the inverter  420 . Specifically, the output voltage detector F may detect each phase output voltage vo output from the inverter. To this end, the output voltage detector F may include a resistor, an amplifier, and the like. The detected output voltage vo, as a pulse type discrete signal, may be input to the inverter controller  430 . 
     The three-phase motor  230  includes a stator and a rotor. All three phase AC voltages of predetermined frequencies are applied to coils of all three phase (a-phase, b-phase, and c-phase) stators to rotate the rotor. 
     For example, the motor  230  can include a surface-mounted permanent-magnet synchronous motor (SMPMSM), an interior permanent magnet synchronous motor (IPMSM), a synchronous reluctance motor (Synrm) and the like. The SMPMSM and IPMSM are permanent magnet synchronous motors (PMSMs) employing a permanent magnet and the Synrm has no permanent magnet. 
     Further, the switching device  450  is disposed between the inverter  420  and the motor  230 , and may switch windings of the motor  230  to a first connection or a second connection. 
     Here, the first connection may be Y-connection, and the second connection may be A-connection. 
     To this end, the switching device  450  may include three relay devices SW 1  to SW 3  respectively connected between three-phase output terminals of the inverter  420  and three-phase coils CA, Cb, and CC. 
     That is, the switching device  450  may include first to third relay devices SW 1  to SW 3  which are electrically connected to the respective phase outputs. 
     If the motor  230  operates at a speed less than or equal to a first speed or a first operating frequency, the switching device  450  may operate for the motor  230  to be in the first connection; and if the motor  230  operates at a speed exceeding the first speed or the first operating frequency, the switching device  450  may operate for the motor  230  to be in the second connection, thereby increasing power conversion efficiency or motor driving efficiency. 
     Particularly, at a low speed less than or equal to the first speed or the first operating frequency, the power conversion efficiency or motor driving efficiency may be improved. 
     Further, the motor driving device  220  according to an embodiment of the present disclosure includes: the switching device  450  disposed between the motor  230  and the inverter  420 ; the controller  170 , which when windings of the motor  230  are switched from the first connection to the second connection, controls the operating frequency of the motor  230  to be less than or equal to the first frequency, and when windings of the motor  230  are switched from the second connection to the first connection, controls the operating frequency of the motor  230  to be less than or equal to a second frequency which is less than the first frequency. Accordingly, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented, as well as burnout of the inverter  420 . A detailed description thereof will be made later with reference to  FIG. 7  and the following figures. 
       FIG. 6  is an internal block diagram illustrating an inverter controller of  FIG. 5 . 
     Referring to  FIG. 6 , the inverter controller  430  may include an axis transformation unit  310 , a speed calculator  320 , a current reference generator  330 , a voltage reference generator  340 , an axis transformation unit  350 , and a switching control signal output unit  360 . 
     The axis transformation unit  310  receives the three-phase output currents i a , i b , and i c  detected by the output current detector E and transforms the received output currents i a , i b , and i c  into two-phase currents i α  and i β  of a stationary coordinate system. 
     Meanwhile, the axis transformation unit  310  may transform the two-phase currents i α  and i β  of the stationary coordinate system into two-phase currents i d  and i q  of a rotating coordinate system. 
     The speed calculator  320  may output a calculated position {circumflex over (θ)}, and a calculated speed {circumflex over (ω)}, based on the two-phase currents i α  and i β  of the stationary coordinate system which is transformed by the axis transformation unit  310 . 
     Meanwhile, the current reference generator  530  generates a current reference value i* q  based on the calculated speed {circumflex over (ω)} r  and a speed reference value ω* r . For example, a PI controller  335  of the current reference generator  330  may perform PI control based on a difference between the calculated speed {circumflex over (ω)} r  and the speed reference value ω* r , and may generate a current reference value i* q . Although a q-axis current reference value i* q  is shown as the current reference value in the figure, it is possible to generate a d-axis current reference value i* d  together with the q-axis current reference value i* q . The d-axis current reference value i d  may be set to 0. 
     Meanwhile, the current reference generator  330  may further include a limiter (not shown) for limiting the level of the current reference value i* q  such that the current reference value i* q  does not exceed an allowable range. 
     The voltage reference generator  340  generates d-axis and q-axis voltage reference values V* d  and V* q  based on d-axis and q-axis currents i d  and i q  axis-transformed into a two-phase rotating coordinate system by the axis transformation unit and the current reference value i* d  and i* q  generated by the current reference generator  330 . For example, a PI controller  344  of the voltage reference generator  340  may perform PI control based on the difference between the q-axis current i q  and the q-axis current reference value i* q  to generate a q-axis voltage reference value V* q . In addition, a PI controller  348  of the voltage reference generator  340  may perform PI control based on the difference between the d-axis current i d  and the d-axis current reference value i* d  to generate a d-axis voltage reference value V* d . The d-axis voltage reference value V* d  may be set to 0 in the case in which the d-axis current reference value i* d  is set to 0. 
     Meanwhile, the voltage reference generator  340  may further include a limiter (not shown) for limiting levels of the d-axis and q-axis voltage reference values V* d  and V* q  such that the d-axis and q-axis voltage reference values V* d  and V* q  do not exceed allowable ranges. 
     Meanwhile, the generated d-axis and q-axis voltage reference values V* d  and V* q  are input to the axis transformation unit  350 . 
     The axis transformation unit  350  receives the calculated position {circumflex over (θ)} r  and the d-axis and q-axis voltage reference values V* d  and V* q  from the position estimator  320  to perform axis transformation. 
     First, the axis transformation unit  350  performs transformation from a two-phase rotating coordinate system to a two-phase stationary coordinate system. At this time, the position {circumflex over (θ)} r  calculated by the position estimator  320  may be used. 
     Subsequently, the axis transformation unit  350  performs transformation from the two-phase stationary coordinate system to a three-phase stationary coordinate system. As a result, the axis transformation unit  350  outputs three-phase output voltage reference values V*a, V*b, and V*c. 
     The switching control signal output unit  360  generates and outputs a PWM-based inverter switching control signal S ic  based on the three-phase output voltage reference values V*a, V*b, and V*c. 
     The output inverter switching control signal S ic  may be converted into a gate driving signal by a gate driver (not shown), and may then be input to a gate of each switching element of the inverter  420 . As a result, the respective switching elements Sa, S′a, Sb, S′b, Sc, and S′c of the inverter  420  perform switching operations. 
     As described above, it is essential for the motor driving apparatus  220  to sense an output current io flowing to the motor, particularly a phase current, in order to perform vector control for driving the motor  230  through control of the inverter  420 . 
     The inverter controller  430  may control the motor  230  to produce a desired speed and a desired torque using the current reference generator  330  and the voltage reference generator  340  based on the sensed phase current. 
       FIG. 7  is a diagram referred to in the description of an operation of a switching device of  FIG. 4 . 
     Referring to the drawing, (a) of  FIG. 7  illustrates an example in which the switching device  450  operates such that the motor  230  operates in Y-connection which is the first connection; and (b) of  FIG. 7  illustrates an example in which the switching device  450  operates such that the motor  230  operates in Δ-connection which is the second connection. 
     The switching device  450  includes the first to third relay devices SW 1  to SW 3  which are electrically connected to the respective phase outputs of the inverter  420 . 
     A first terminal naa of the first relay device SW 1 , a first terminal nba of the second relay device SW 2 , and a first terminal nca of the third relay device SW 3  are connected in parallel, in which one end nA of a first winding CA of the motor  230  is connected to the second terminal nab of the first relay device SW 1 ; one end nB of a second winding CB of the motor  230  is connected to the second terminal nbb of the second relay device SW 2 ; one end nC of a third winding CC of the motor  230  is connected to the second terminal ncb of the third relay device SW 3 ; the other end na of the first winding CA of the motor  230  is connected to a common terminal n 3  of the third relay device SW 3 ; the other end nb of the second winding CB of the motor  230  is connected to a common terminal n 1  of the first relay device SW 1 ; and the other end nc of the third winding CC of the motor  230  is connected to the common terminal n 2  of the second relay device SW 2 . 
     The second terminal nab of the first relay device SW 1  is connected to a U-phase output terminal ru of the inverter  420 , and the second terminal nbb of the second relay device SW 2  is connected to a V-phase output terminal rv of the inverter  420 , and the second terminal ncb of the third relay device SW 3  is connected to a W-phase output terminal rw of the inverter  420 . 
     As illustrated in (a) of  FIG. 7 , for the first connection, the controller  170  may control the common terminals n 1 , n 2 , and n 3  of the first to third relay devices SW 1  to SW 3  to be electrically connected to the respective first terminals naa, nba, and nca of the first to third relay devices SW 1  to SW 3 . 
     In this manner, output currents of the U-, V-, and W-phases of the inverter  420  may respectively flow through the a-phase coil CA, the b-phase coil CB, and the c-phase coil CC of the motor  230  which is in Y-connection. 
     As illustrated in (b) of  FIG. 7 , for the second connection, the controller  170  may control the common terminals n 1 , n 2 , and n 3  of the first to third relay devices SW 1  to SW 3  to be electrically connected to the respective second terminals nab, nbb, and ncb of the first to third relay devices SW 1  to SW 3 . 
     In this manner, output currents of the U-, V-, and W-phases of the inverter  420  may respectively flow through the b-phase coil CB, the c-phase coil CC, and the a-phase coil CA of the motor  230  which is in Δ-connection. 
     As a result, by the switching device  450 , it is possible to control the motor  230  to operate in the first connection or the second connection, thereby increasing power conversion efficiency or driving efficiency of the motor  230 . 
       FIGS. 8A and 8B  are timing diagrams illustrating a winding switching operation of the switching device of  FIG. 7 . 
     First,  FIG. 8A  is a timing diagram illustrating an example of a winding switching operation of the switching device of  FIG. 7 . 
     Referring to the drawing, when an operating frequency of the motor  230  is less than f 1 , the switching device  450  may operate for the motor  230  to be in Y-connection as illustrated in (a) of  FIG. 7 . 
     In the drawing, an example is illustrated in which during a period Pix up to a time point Txa, the switching device  450  operates for the motor  230  to be in Y-connection. 
     Then, during a period Px from Txa to Txb, the motor  230  may be stopped. 
     Subsequently, during a period P 2   x  after the time point Txb, the switching device  450  may operate for the motor  230  to be in Δ-connection as illustrated in (b) of  FIG. 7 . 
     For example, if an operating frequency of the motor  230  exceeds f 1 , the switching device  450  may operate for the motor  230  to be in Δ-connection; and during the period Px, the motor  230  may be stopped for Y to A conversion. 
     Next,  FIG. 8B  is a timing diagram illustrating another example of a winding switching operation of the switching device. 
     Referring to the drawing, when an operating frequency of the motor  230  is less than or equal to f 1 , the switching device  450  may operate for the motor  230  to be in Y-connection. 
     In the drawing, an example is illustrated in which during a period P 1  up to a time point Ta, the switching device  450  operates for the motor  230  to be in Y-connection. 
     Then, during a period P 2  from Ta to Tb, the controller  170  or the inverter controller  430  may control windings of the motor  230  to be switched from the first connection to the second connection. 
     Particularly, the controller  170  or the inverter controller  430  may control the motor  230  not to stop during the period P 2 , and may control an operating frequency of the motor  230  to temporarily decrease from the first frequency f 1  to the second frequency f 2 . 
     Subsequently, during a period P 3  after the time period Tb, the switching device  450  may operate for the motor  230  to be in Δ-connection as illustrated in (b) of  FIG. 7 . 
     For example, if an operating frequency of the motor  230  exceeds f 1 , the controller  170  or the inverter controller  430  may control the switching device  450  to operate for the motor  230  to be in Δ-connection. 
     Specifically, during the period P 3 , the controller  170  or the inverter controller  430  may control the operating frequency of the motor  230 , which is temporarily decreased to the second frequency f 2 , to increase again. 
     The controller  170  of the inverter controller  430  may control the motor  230  to operate continuously without stopping while the switching device  450  switches the windings of the motor  230  from the first connection to the second connection. In this manner, the motor  230  does not stop during the switching operation of the switching device  450 , such that an operating efficiency of the motor  230  may be improved. 
     In this case, the period P 2  of  FIG. 8B  is preferably shorter than the period Px of  FIG. 8A . Accordingly, by temporarily decreasing the speed of the motor  230 , the windings of the motor  230  may be switched from the first connection to the second connection. 
       FIGS. 9A to 9I  are diagrams referred to in the description of a switching device of  FIG. 4 . 
     First,  FIG. 9A  illustrates an example in which the motor  230  is in the first connection, and an operating frequency of the motor  230  is fx. 
     Referring to the drawing, when the windings of the motor  230  are connected in the first connection, and the operating frequency of the motor  230  is fx, if an output of the inverter  420  is stopped or decreased for switching to the second connection, a regenerative current Irfa may pass through the switching device  450  and the inverter  420  to flow to the DC terminal capacitor C. 
     Accordingly, a dc terminal voltage, which is a voltage at both ends of the DC terminal capacitor C, may increase to Vdca 1 . 
     However, the regenerative current Irfa may increase the possibility of burnout of the DC terminal. Further, the regenerative current Irfa may also increase the possibility of burnout of the switching device  450 , the inverter  420 , and the like. 
     Particularly, as the operating frequency of the motor  230  increases, the possibility of burnout of the DC terminal capacitor C, the switching device  450 , the inverter  420 , and the like may also increase. 
     In order to reduce the possibility of burnout of the circuit device, a brake chopper circuit  415  operates when a dc terminal voltage exceeds an allowable voltage. 
       FIG. 9B  illustrates an example in which the brake chopper circuit  415  operates when the windings of the motor  230  are connected in the first connection, and the operating frequency of the motor is fx. 
     For example, if a do terminal voltage Vdca 1  of  FIG. 9A  exceeds an allowable voltage, the switching element Sp in the brake chopper circuit  415  is switched from an OFF state to an ON state, and as the switching element Sp is turned on, a portion Iova of the current from the DC terminal capacitor C flows through the switching element Sp and the resistor element Rp in the brake chopper circuit  415 . 
     Accordingly, the dc terminal voltage may decrease to a voltage Vdca 2  which is lower than Vdca 1  of  FIG. 9A . 
     As the switching element Sp is turned on, another portion Ika of the current from the DC terminal capacitor C flows to the inverter  420  and the switching device  450 . Due to the current Ika, the possibility of burnout of the switching device  450  may increase. 
     Accordingly, the present disclosure provides a method of reducing the possibility of burnout of the switching device  450  by the flow of the regenerative current or a portion of the dc terminal current. Particularly, the present disclosure provides a method of controlling the regenerative current not to occur or a level of the regenerative current to decrease during switching of connection by the switching device  450  for the dc terminal voltage not to exceed an allowable voltage. 
       FIG. 9C  illustrates an example in which windings of the motor  230  are connected in the first connection, and the operating frequency of the motor  230  is f 1  which is less than fx. 
     Referring to the drawing, when the windings of the motor  230  are switched from the first connection to the second connection, the controller  170  or the inverter controller  430  may control the operating frequency of the motor  230  to be f 1  which is less than fx. 
     Accordingly, a regenerative current at a level lower than Irfa of  FIG. 9A  may flow to the DC terminal capacitor C through the switching device  450  and the inverter  420 . 
     Meanwhile, a dc terminal voltage, which is a voltage at both ends of the DC terminal capacitor C, may be Vdca 3  which is less than Vdca 1  of  FIG. 9A . In this case, Vdca 3  is preferably less than or equal to an allowable voltage. 
     Accordingly, the brake chopper circuit  415  at the dc terminal does not operate during the operation of the switching device  450 . 
     By the regenerative current Irfa 2 , the possibility of burnout of the DC terminal capacitor C may be reduced significantly, as well as the possibility of burnout of the switching device  450 , the inverter  420 , and the like. 
     That is, the controller  170  or the inverter controller  430  according to the embodiment of the present disclosure may control the operating frequency of the motor  230  to be less than or equal to the first frequency f 1  when the motor  230  is switched from the first connection to the second connection. In this manner, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented, as well as burnout of the inverter  420 . 
     Similarly to  FIG. 9C ,  FIG. 9D  illustrates an example in which the windings of the motor  230  are connected in the first connection, and the operating frequency of the motor  230  is f 1  which is less than fx. 
     Referring to the drawing, when the windings of the motor  230  are switched from the first connection to the second connection, the controller  170  or the inverter controller  430  may control the operating frequency of the motor  230  to be f 1  which is less than fx. 
     Meanwhile, there is a difference in that unlike  FIG. 9C , no regenerative current flows in  FIG. 9D . 
     Accordingly, the dc terminal voltage, which is a voltage at both ends of the DC terminal capacitor C, may be Vdca 4  which is less than Vdca 3 . 
     In this case, Vdca 4  is less than or equal to an allowable voltage, such that the brake chopper circuit  415  at the dc terminal does not operate during the operation of the switching device  450 . 
     As a result, the possibility of burnout of the switching device  450 , the inverter  420 , and the like may be reduced significantly. 
     Then,  FIG. 9E  illustrates an example in which the windings of the motor  230  are connected in the second connection, and the operating frequency of the motor  230  is fy. 
     Referring to the drawing, when the windings of the motor  230  are connected in the second connection, and the operating frequency of the motor  230  is fy, if an output of the inverter  420  is stopped or decreased for switching to the first connection, a regenerative current Irfb may flow to the DC terminal capacitor C through the switching device  450  and the inverter  420 . 
     Accordingly, the dc terminal voltage, which is a voltage at both ends of the DC terminal capacitor C, may increase to Vdcb 1 . 
     In this case, the regenerative current Irfb may increase the possibility of burnout of the DC terminal capacitor C. Further, the regenerative current Irfb may also increase the possibility of burnout of the switching device  450 , the inverter  420 , and the like. 
     Particularly, as the operating frequency of the motor  230  increases, the possibility of burnout of the DC terminal capacitor C, the switching device  450 , the inverter  420 , and the like may also increase. 
     In order to reduce the possibility of burnout of the circuit device, the brake chopper circuit  415  operates if a dc terminal voltage exceeds an allowable voltage. 
       FIG. 9F  illustrates an example in which the brake chopper circuit  415  operates when the windings of the motor  230  are connected in the second connection, and the operating frequency of the motor is fy. 
     For example, if a dc terminal voltage Vdcb 1  of  FIG. 9E  exceeds an allowable voltage, the switching element Sp in the brake chopper circuit  415  is switched from an OFF state to an ON state, and as the switching element Sp is turned on, a portion Iovb of the current from the DC terminal capacitor C flows through the switching element Sp and the resistor element Rp in the brake chopper circuit  415 . 
     In this manner, the dc terminal voltage may decrease to a voltage Vdcb 2  which is less than Vdcb 1  of  FIG. 9E . 
     As the switching element Sp is turned on, another portion Ikb of the current from the DC terminal capacitor C flows to the inverter  420  and the switching device  450 . Due to the current Ikb, the possibility of burnout of the switching device  450  may increase. 
     Accordingly, the present disclosure provides a method of reducing the possibility of burnout of the switching device  450  by the flow of the regenerative current or a portion of the dc terminal current of  FIGS. 9E and 9F . Particularly, the present disclosure provides a method of controlling the regenerative current not to occur or a level of the regenerative current to decrease during switching of connection by the switching device  450 , so that the dc terminal voltage does not exceed an allowable voltage. 
       FIG. 9G  illustrates an example in which the windings of the motor  230  are connected in the second connection, and the operating frequency of the motor  230  is f 2  which is less than fy. 
     Referring to the drawing, when the windings of the motor  230  are switched from the second connection to the first connection, the controller  170  or the inverter controller  430  may control the operating frequency of the motor  230  to be f 2  which is less than fy. 
     Accordingly, a regenerative current Irfb 2  at a level lower than Irfb of  FIG. 9E  may flow to the DC terminal capacitor C through the switching device  450  and the inverter  420 . 
     Meanwhile, a dc terminal voltage, which is a voltage at both ends of the DC terminal capacitor C, may be Vdca 3  which is less than Vdcb 1  of  FIG. 9E . In this case, Vdca 3  is preferably less than or equal to an allowable voltage. 
     Accordingly, the brake chopper circuit  415  at the dc terminal does not operate during the operation of the switching device  450 . 
     By the regenerative current Irfb 2 , the possibility of burnout of the DC terminal capacitor C may be reduced significantly, as well as the possibility of damage to the switching device  450 , the inverter  420 , and the like. 
     Meanwhile, in the first connection which is Y-connection, an induced voltage or a counter electromotive force is approximately √{square root over (3)} times greater than in the second connection which is A connection, such that a maximum operating frequency of the motor  230  in the first connection is preferably greater than a maximum operating frequency of the motor  230  in the second connection. 
     Accordingly, during switching from the second connection to the first connection, the controller  170  or the inverter controller  430  preferably controls the operating frequency of the motor  230  to be less than or equal to the second frequency f 2  which is less than the first frequency f 1 . 
     Accordingly, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented, as well as burnout of the inverter  420 . 
     Similarly to  FIG. 9G ,  FIG. 9H  illustrates an example in which the windings of the motor  230  are connected in the second connection, and the operating frequency of the motor  230  is f 2  which is less than fy. 
     Referring to the drawing, when the windings of the motor  230  are switched from the second connection to the first connection, the controller  170  or the inverter controller  430  may control the operating frequency of the motor  230  to be f 2  which is less than fy. 
     Meanwhile, there is a difference in that unlike  FIG. 9G , no regenerative current flows in  FIG. 9H . 
     Accordingly, the dc terminal voltage, which is a voltage at both ends of the DC terminal capacitor C, is Vdcb 4  which is less than Vdcb 3  of  FIG. 9G . 
     In this case, Vdcb 4  is less than or equal to an allowable voltage, such that the brake chopper circuit  415  at the dc terminal does not operate during the operation of the switching device  450 . 
     As a result, the possibility of burnout of the switching device  450 , the inverter  420 , and the like may be reduced significantly. 
       FIG. 9I  illustrates a graph CV 1  showing a dc terminal voltage change with respect to frequency in the first connection, and a graph CV 2  showing a dc terminal voltage change with respect to frequency in the first connection. 
     Referring to the drawing, as the operating frequency of the motor increases, an increasing rate of the dc terminal voltage in the first connection is greater than an increasing rate of the dc terminal voltage in the second connection. 
     Meanwhile, Vdcf in the drawing may indicate an allowable voltage of the dc voltage, in which Vdcf may be approximately in a range of 700 V to 800 V. 
     Meanwhile, as the increasing rate of the dc terminal voltage in the first connection is greater than the increasing rate of the dc terminal voltage in the second connection, if the dc terminal voltage, such as Arx, in the first connection exceeds the allowable voltage Vdcf, the possibility of burnout of the switching device  450  and the like may increase due to the regenerative current or the dc terminal current. 
     Accordingly, in the present disclosure, during switching from the first connection to the second connection by the operation of the switching device  450 , the motor  230  is controlled to operate with the dc terminal voltage at a frequency less than or equal to the first frequency f 1  which is a maximum frequency not exceeding the allowable voltage Vdcf. 
     Similarly, in the present disclosure, during switching from the second connection to the first connection by the operation of the switching device  450 , the motor  230  is controlled to operate with the dc terminal voltage at a frequency less than or equal to a second frequency f 2  which is a maximum frequency not exceeding the allowable voltage Vdcf, which will be described below with reference to  FIG. 10 . 
       FIG. 10  is a flowchart illustrating an operating method of a motor driving apparatus according to an embodiment of the present disclosure. 
     Referring to the drawing, the controller  170  or the inverter controller  430  determines whether switching from the first connection to the second connection is required (S 1010 ). 
     For example, is the motor  230  is required to operate at a speed exceeding the first speed, the controller  170  or the inverter controller  430  may determine that switching from the first connection to the second connection is required. 
     Accordingly, as illustrated in  FIG. 9C or 9D , the controller  170  or the inverter controller  430  may control the operating frequency of the motor  230  to be less than or equal to the first frequency f 1  (S 1020 ). 
     In this manner, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented, as well as burnout of the inverter  420 . 
     Meanwhile, if the windings of the motor  230  are switched from the first connection to the second connection, the controller  170  or the inverter controller  430  may control the operating frequency of the motor  230  to be less than or equal to the first frequency f 1  so that the detected dc terminal voltage Vdc may be less than or equal to an allowable voltage, as illustrated in  FIG. 9C or 9D . Accordingly, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented, as well as burnout of the inverter  420 . 
     Meanwhile, if the windings of the motor  230  are switched from the first connection to the second connection, the controller  170  or the inverter controller  430  may control an output of the inverter  420  to be stopped as illustrated in  FIG. 9C or 9D . After the output of the inverter  420  is stopped, a regenerative current from the motor  230  is supplied to the dc terminal through the switching device  450  and the inverter  420 . The controller  170  or the inverter controller  430  may control control the operating frequency of the motor  230  to be less than or equal to the first frequency f 1  during the supply of the regenerative current for the detected dc terminal voltage Vdc to be less than or equal to the allowable voltage. Accordingly, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented, as well as burnout of the inverter  420 . 
     Meanwhile, if the windings of the motor  230  are switched from the first connection to the second connection, the controller  170  or the inverter controller  430  may control the operating frequency of the motor  230  to decrease to the first frequency f 1  or less as illustrated in  FIG. 9C or 9D  so that the switching element Sp in the brake chopper circuit  415  may not be turned on. Accordingly, it is possible to control the brake chopper circuit  415  at the dc terminal not to operate during the operation of the switching device  450 , thereby preventing burnout of the switching device  450  for switching connection of windings of the motor  230 . 
     Meanwhile, if the windings of the motor  230  are switched from the first connection to the second connection, the controller  170  or the inverter controller  430  may control an output of the inverter  420  to be stopped as illustrated in  FIG. 9C or 9D . After the output of the inverter  420  is stopped, the controller  170  or the inverter controller  430  may control a first regenerative current from the motor  230  to be supplied to the dc terminal, and then a second regenerative current, which is lower than the first regenerative current, to be supplied to the dc terminal for the switching element Sp in the brake chopper circuit  415  not to be turned on. In this manner, it is possible to control the brake chopper circuit  415  not to operate during the operation of the switching device  450 . As a result, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented. 
     Then, the controller  170  or the inverter controller  430  may complete switching from the first connection to the second connection (S 1030 ). That is, the controller  170  or the inverter controller  430  may control switching from (a) to (b) of  FIG. 7 . 
     Meanwhile, the controller  170  or the inverter controller  430  determines whether switching from the second connection to the first connection is required (S 1040 ). 
     For example, if the motor  230  is required to operate at a speed less than or equal to the first speed, the controller  170  or the inverter controller  430  may determine that switching from the second connection to the first connection is required. 
     Accordingly, the controller  170  or the inverter controller  430  may control the operating frequency of the motor  230  to be less than or equal to a second frequency f 2  which is less than the first frequency f 1  (S 1050 ). 
     In this manner, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented, as well as burnout of the inverter  420 . 
     Meanwhile, if the windings of the motor  230  are switched from the second connection to the first connection, the controller  170  or the inverter controller  430  may control the operating frequency of the motor  230  to be less than or equal to the second frequency f 2  as illustrated in  FIG. 9G or 9H , so that the detected dc terminal voltage Vdc is less than or equal to the allowable voltage. In this manner, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented, as well as burnout of the inverter  420 . 
     Meanwhile, if the windings of the motor  230  are switched from the second connection to the first connection, the controller  170  or the inverter controller  430  may control an output of the inverter  420  to be stopped as illustrated in  FIG. 9G or 9H . After the output of the inverter  420  is stopped, a regenerative current from the motor  230  is supplied to the dc terminal through the switching device  450  and the inverter  420 . The controller  170  or the inverter controller  430  may control the operating frequency of the motor  230  to be less than or equal to the second frequency f 2  during the supply of the regenerative current for the detected dc terminal voltage Vdc to be less than or equal to the allowable voltage. In this manner, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented, as well as burnout of the inverter  420 . 
     Meanwhile, if the windings of the motor  230  are switched from the second connection to the first connection, the controller  170  or the inverter controller  430  may control the operating frequency of the motor  230  to decrease to the second frequency f 2  or less as illustrated in  FIG. 9G or 9H  so that the switching element Sp in the brake chopper circuit  415  may not be turned on. Accordingly, it is possible to control the brake chopper circuit  415  at the dc terminal not to operate during the operation of the switching device  450 . As a result, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented. 
     Meanwhile, if the windings of the motor  230  are switched from the second connection to the first connection, the controller  170  or the inverter controller  430  may control an output of the inverter  420  to be stopped as illustrated in  FIG. 9G or 9H . After the output of the inverter  420  is stopped, the controller  170  or the inverter controller  430  may control a third regenerative current from the motor  230  to be supplied to the dc terminal, and then a fourth regenerative current, which is lower than the third regenerative current, to be supplied to the dc terminal for the switching element Sp in the brake chopper circuit  415  not to be turned on. In this manner, it is possible to control the brake chopper circuit  415  not to operate during the operation of the switching device  450 . As a result, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented. 
     Then, the controller  170  or the inverter controller  430  may complete switching from the second connection to the first connection (S 1060 ). That is, the controller  170  or the inverter controller  430  may control switching from (b) to (a) of  FIG. 7 . 
     Meanwhile, if the windings of the motor  230  are switched from the first connection to the second connection, the controller  170  or the inverter controller  430  may control the operating frequency of the motor  230  to be greater than or equal to a first reference frequency, and if the windings of the motor  230  are switched from the second connection to the first connection, the controller  170  or the inverter controller  430  may control the operating frequency of the motor  230  to be greater than or equal to a second reference frequency. 
     That is, if the windings of the motor  230  are switched from the first connection to the second connection, the controller  170  or the inverter controller  430  may control a minimum operating frequency of the motor  230  to be the first reference frequency, and if the windings of the motor  230  are switched from the second connection to the first connection, the controller  170  or the inverter controller  430  may control a minimum operating frequency of the motor  230  to be the second reference frequency. 
     In this case, the first reference frequency may be greater than the first reference frequency. Alternatively, the first reference frequency may be equal to the second reference frequency, which will be described below with reference to  FIG. 11 . 
       FIG. 11  illustrates an operating frequency range of the motor  230  when windings of the motor  230  are switched from the first connection to the second connection, and an operating frequency range of the motor  230  when windings of the motor  230  are switched from the second connection to the first connection. 
     Referring to the drawing, (a) of  FIG. 11  illustrates an operating frequency range of f 0  to f 1  of the motor  230  during switching from the first connection to the second connection. 
     Referring to the drawing, (b) of  FIG. 11  illustrates an operating frequency range of f 0  to f 2  of the motor  230  during switching from the second connection to the first connection. 
     Meanwhile, an induced voltage or a counter electromotive force is greater in the first connection than in the second connection, the controller  170  or the inverter controller  430  may control the operating frequency range of f 0  to f 1  of the motor  230 , during switching of the windings of the motor  230  from the first connection to the second connection, to be greater than the operating frequency range of f 0  to f 2  of the motor  230  during switching from the second connection to the first connection. Accordingly, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented, as well as burnout of the inverter  420 . 
       FIG. 12A  illustrates an example in which during switching from the first connection to the second connection, the operating frequency of the motor  230  is the first frequency f 1 , such that burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented. 
       FIG. 12B  illustrates an example in which during switching from the second connection to the first connection, the operating frequency of the motor  230  is the second frequency f 2 , such that burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented. 
       FIG. 13A  illustrates a UV line-to-line voltage waveform CUVa, a dc terminal voltage waveform Vdca, and a U-phase current waveform Iua in the case where the brake chopper circuit  415  operates during switching from the first connection to the second connection, as illustrated in  FIG. 9B . 
     For example, when the motor  230  operates at the operating frequency fx, which exceeds the maximum operating frequency f 1 , the brake chopper circuit  415  operates as illustrated in  FIG. 9B . 
     In an interval Ppa 1 , in which the switching element Sp of the brake chopper circuit  415  is switched from OFF to ON, peak components, such as Ara 1 , Ara 2 , and Ara 3 , occur in the UV line-to-line voltage waveform CUVa, the dc terminal voltage waveform Vdca, and the U-phase current waveform Iua, respectively. Accordingly, the possibility of burnout of the switching device  450  and the inverter  240  may increase. 
     Meanwhile, in an interval Ppa 2  following the interval Ppa 1 , the switching element Sp of the brake chopper circuit  415  is maintained in an ON state, such that no peak component occurs in the UV line-to-line voltage waveform CUVa, the dc terminal voltage waveform Vdca, and the U-phase current waveform Iua. 
       FIG. 13B  illustrates a UV line-to-line voltage waveform CUVb, a dc terminal voltage waveform Vdcb, and a U-phase current waveform Iub in the case where the brake chopper circuit  415  does not operate during switching from the first connection to the second connection, as illustrated in  FIG. 9C or 9D . 
     For example, in the case where the motor  230  operates at the operating frequency f 1 , which is the maximum operating frequency, the brake chopper circuit  415  does not operate as illustrated in  FIG. 9C or 9D . 
     Accordingly, unlike  FIG. 13A , during the intervals Ppb 1  and Ppb 2 , no peak component occurs in the UV line-to-line voltage waveform CUVa, the dc terminal voltage waveform Vdca, and the U-phase current waveform Iua, such that the possibility of burnout of the switching device  450  and the inverter  420  may be significantly reduced. 
       FIG. 14  is a flowchart illustrating an operating method of a motor driving apparatus according to another embodiment of the present disclosure. 
     Referring to the drawing, the controller  170  or the inverter controller  430  determines whether switching from the first connection to the second connection is required (S 1310 ). 
     For example, is the motor  230  is required to operate at a speed exceeding the first speed, the controller  170  or the inverter controller  430  may determine that switching from the first connection to the second connection is required. 
     Accordingly, the controller  170  or the inverter controller  430  may control the operating frequency of the motor  230  to be greater than or equal to the first reference frequency (S 1320 ). 
     In this manner, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented, as well as burnout of the inverter  420 . 
     Then, the controller  170  or the inverter controller  430  may complete switching from the first connection to the second connection (S 1330 ). That is, the controller  170  or the inverter controller  430  may control switching from (a) to (b) of  FIG. 7 . 
     Meanwhile, the controller  170  or the inverter controller  430  determines whether switching from the second connection to the first connection is required (S 1340 ). 
     For example, if the motor  230  is required to operate at a speed less than or equal to the first speed, the controller  170  or the inverter controller  430  may determine that switching from the second connection to the first connection is required. 
     Accordingly, the controller  170  or the inverter controller  430  may control the operating frequency of the motor  230  to be greater than or equal to a second reference frequency (S 1350 ). 
     Meanwhile, the first reference frequency may be greater than the second reference frequency. Alternatively, the first reference frequency may be equal to the second reference frequency, as illustrated in  FIG. 11 . 
     Then, the controller  170  or the inverter controller  430  may complete switching from the second connection to the first connection (S 1360 ). That is, the controller  170  or the inverter controller  430  may control switching from (b) to (a) of  FIG. 7 . 
       FIG. 15  is a flowchart illustrating an operating method of a motor driving apparatus according to another embodiment of the present disclosure; and  FIG. 16  is a diagram referred to in the description of the operation of  FIG. 15 . 
     Referring to the drawing, the controller  170  or the inverter controller  430  determines whether switching from the first connection to the second connection is required (S 1410 ). 
     For example, if the motor  230  is required to operate at a speed exceeding the first speed, the controller  170  or the inverter controller  430  may determine that the switching from the first connection to the second connection is required. 
     Accordingly, the controller  170  or the inverter controller  430  may control temperature of the inverter  420  to be less than or equal to a first reference temperature T 1  (S 1420 ). 
     In this manner, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented, as well as burnout of the inverter  420 . 
     Meanwhile, if the windings of the motor  230  are switched from the first connection to the second connection, the controller  170  or the inverter controller  430  may control temperature of the inverter  420  to be less than or equal to the first reference temperature T 1 . Accordingly, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented, as well as burnout of the inverter  420 . 
     Meanwhile, if the windings of the motor  230  are switched from the first connection to the second connection, the controller  170  or the inverter controller  430  may control an output of the inverter  420  to be stopped as illustrated in  FIG. 9C or 9D . After the output of the inverter  420  is stopped, a regenerative current from the motor  230  is supplied to the dc terminal through the switching device  450  and the inverter  420 . The controller  170  or the inverter controller  430  may control temperature of the inverter  420  to be less than or equal to the first reference temperature T 1  during the supply of the regenerative current for the detected dc terminal voltage Vdc to be less than or equal to the allowable voltage. Accordingly, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented, as well as burnout of the inverter  420 . 
     Meanwhile, if the windings of the motor  230  are switched from the first connection to the second connection, the controller  170  or the inverter controller  430  may control temperature of the inverter  420  to be less than or equal to the first reference temperature T 1  as illustrated in  FIG. 9C or 9D , so that the switching element Sp in the brake chopper circuit  415  may not be turned on. Accordingly, it is possible to control the brake chopper circuit  415  at the dc terminal not to operate during the operation of the switching device  450 . As a result, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented. 
     Meanwhile, if the windings of the motor  230  are switched from the first connection to the second connection, the controller  170  or the inverter controller  430  may control an output of the inverter  420  to be stopped as illustrated in  FIG. 9C or 9D . After the output of the inverter  420  is stopped, the controller  170  or the inverter controller  430  may control a first regenerative current from the motor  230  to be supplied to the dc terminal, and then a second regenerative current, which is lower than the first regenerative current, to be supplied to the dc terminal for the switching element Sp in the brake chopper circuit  415  not to be turned on. In this manner, it is possible to control the brake chopper circuit  415  not to operate during the operation of the switching device  450 . As a result, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented. 
     Then, the controller  170  or the inverter controller  430  may complete switching from the first connection to the second connection (S 1430 ). That is, the controller  170  or the inverter controller  430  may control switching from (a) to (b) of  FIG. 7 . 
     Meanwhile, the controller  170  or the inverter controller  430  determines whether switching from the second connection to the first connection is required (S 1440 ). 
     For example, if the motor  230  is required to operate at a speed less than or equal to the first speed, the controller  170  or the inverter controller  430  may determine that switching from the second connection to the first connection is required. 
     Accordingly, the controller  170  or the inverter controller  430  may control temperature of the inverter  420  to be less than or equal to a second reference temperature T 2  which is lower than the first reference temperature T 1  (S 1450 ), as illustrated in  FIG. 9G or 9H . 
     In this manner, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented. 
     Meanwhile, if the windings of the motor  230  are switched from the second connection to the first connection, the controller  170  or the inverter controller  430  may control temperature of the inverter  420  to be less than or equal to the second reference temperature T 2  as illustrated in  FIG. 9G or 9H , so that the detected dc terminal voltage Vdc is less than or equal to the allowable voltage. Accordingly, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented, as well as burnout of the inverter  420 . 
     Meanwhile, if the windings of the motor  230  are switched from the second connection to the first connection, the controller  170  or the inverter controller  430  may control an output of the inverter  420  to be stopped as illustrated in  FIG. 9G or 9H . After the output of the inverter  420  is stopped, a regenerative current from the motor  230  is supplied to the dc terminal through the switching device  450  and the inverter  420 . The controller  170  or the inverter controller  430  may control temperature of the inverter  420  to be less than or equal to the second reference temperature T 2  during the supply of the regenerative current for the detected dc terminal voltage Vdc to be less than or equal to the allowable voltage. Accordingly, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented, as well as burnout of the inverter  420 . 
     Meanwhile, if the windings of the motor  230  are switched from the second connection to the first connection, the controller  170  or the inverter controller  430  may control temperature of the inverter  420  to decrease to the second reference temperature T 2  or less as illustrated in  FIG. 9G  or  9 H so that the switching element Sp in the brake chopper circuit  415  may not be turned on. Accordingly, it is possible to control the brake chopper circuit  415  at the dc terminal not to operate during the operation of the switching device  450 . As a result, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented. 
     Meanwhile, if the windings of the motor  230  are switched from the second connection to the first connection, the controller  170  or the inverter controller  430  may control an output of the inverter  420  to be stopped as illustrated in  FIG. 9G or 9H . After the output of the inverter  420  is stopped, the controller  170  or the inverter controller  430  may control a third regenerative current from the motor  230  to be supplied to the dc terminal, and then a fourth regenerative current, which is lower than the third regenerative current, to be supplied to the dc terminal for the switching element Sp in the brake chopper circuit  415  not to be turned on. In this manner, it is possible to control the brake chopper circuit  415  not to operate during the operation of the switching device  450 . As a result, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented. 
     Then, the controller  170  or the inverter controller  430  may complete switching from the second connection to the first connection (S 1460 ). That is, the controller  170  or the inverter controller  430  may control switching from (b) to (a) of  FIG. 7 . 
     Meanwhile, if the windings of the motor  230  are switched from the first connection to the second connection, the controller  170  or the inverter controller  430  may control temperature of the inverter  420  to be greater than or equal to a first minimum temperature, and if the windings of the motor  230  are switched from the second connection to the first connection, the controller  170  or the inverter controller  430  may control temperature of the inverter  420  to be greater than or equal to a second minimum temperature. 
     In this case, the first minimum temperature may be greater than the second minimum temperature. Alternatively, the first minimum temperature may be equal to the second minimum temperature, which will be described below with reference to  FIG. 16 . 
       FIG. 16  illustrates an operable temperature range of the inverter  420  during switching from the first connection to the second connection, and an operable temperature range of the inverter  420  during switching from the second connection to the first connection. 
     Referring to the drawing, (a) of  FIG. 16  illustrates an operable temperature range of T 0  to T 1  of the inverter  420  during from the first connection to the second connection. 
     Further, (b) of  FIG. 16  illustrates an operable temperature range of T 0  to T 2  of the inverter  420  during switching from the second connection to the first connection. 
     As an induced voltage or a counter electromotive force is greater in the first connection than in the second connection, the controller  170  or the inverter controller  430  may control the operable temperature range of T 0  to T 1  of the inverter  420 , during switching of the windings of the motor  230  from the first connection to the second connection, to be greater than the operable temperature range of T 0  to T 2  of the inverter  420  during switching from the second connection to the first connection. Accordingly, burnout of the switching device  450  for switching connection of windings of the motor  230  may be prevented, as well as burnout of the inverter  420 . 
     The motor driving apparatus  220  according to the embodiments of the present disclosure described above with reference to  FIGS. 4 to 16  may be applied to various home appliances, in addition to the air conditioner  100  of  FIG. 1 . For example, the motor driving apparatus  220  may be applied in various fields, such as a laundry handling apparatus (washing machine, dryer, etc.), a refrigerator, a water purifier, a robot cleaner, a robot, a vehicle, a drone, and the like. 
     The motor driving apparatus and the air conditioner including the same according to an embodiment of the present disclosure may include: a switching device disposed between an inverter and a motor; and a controller, which in response to the windings of the motor being switched from the first connection to the second connection, controls an operating frequency of the motor to be less than or equal to a first frequency, and in response to the windings of the motor being switched from the second connection to the first connection, controls an operating frequency of the motor to be less than or equal to a second frequency which is less than the first frequency. Accordingly, burnout of the switching device for switching connection of the motor windings may be prevented, as well as burnout of the inverter. 
     Meanwhile, the motor driving apparatus and the air conditioner including the same according to an embodiment of the present disclosure may further include: a DC terminal capacitor configured to store a DC terminal voltage; a DC terminal voltage detector configured to detect the DC terminal voltage; and a brake chopper circuit connected to both ends of the DC terminal capacitor and having a resistor and a switching element. Accordingly, burnout of the switching device for switching connection of the motor windings may be prevented, as well as burnout of the inverter. 
     Meanwhile, in response to the windings of the motor being switched from the first connection to the second connection, the controller may control the operating frequency of the motor to be less than or equal to the first frequency for the detected DC terminal voltage to be less than or equal to an allowable voltage. Accordingly, burnout of the switching device, switching connection of the motor windings, may be prevented as well as burnout of the inverter. 
     Meanwhile, in response to the windings of the motor being switched from the first connection to the second connection, the controller controls an output of the inverter to be stopped, wherein after the output of the inverter is stopped, a regenerative current from the motor is supplied to the DC terminal through the switching device and the inverter, and wherein the controller controls the operating frequency of the motor to be less than or equal to the first frequency during the supply of the regenerative current for the detected DC terminal voltage to be less than or equal to the allowable voltage. Accordingly, burnout of the switching device for switching connection of the motor windings may be prevented, as well as burnout of the inverter. 
     Meanwhile, in response to the windings of the motor being switched from the first connection to the second connection, the controller may control the operating frequency of the motor to decrease to the first frequency or less for the switching element in the brake chopper circuit not to be turned on. Accordingly, burnout of the switching device for switching connection of the motor windings may be prevented, as well as burnout of the inverter. 
     Meanwhile, in response to the windings of the motor being switched from the first connection to the second connection, the controller may control an output of the inverter to be stopped, and may control a first regenerative current from the motor to be supplied to the DC terminal, and then a second regenerative current, which is lower than the first regenerative current, to be supplied to the DC terminal for the switching element in the brake chopper circuit not to be turned on that after the output of the inverter is stopped. Accordingly, burnout of the switching device for switching connection of the motor windings may be prevented, as well as burnout of the inverter. 
     Meanwhile, in response to the windings of the motor being switched from the second connection to the first connection, the controller may control the operating frequency of the motor to be less than or equal to the second frequency for the detected DC terminal voltage to be less than or equal to the allowable range. Accordingly, burnout of the switching device for switching connection of the motor windings may be prevented, as well as burnout of the inverter. 
     Meanwhile, in response to the windings of the motor being switched from the second connection to the first connection, the controller may control an output of the inverter to be stopped, and wherein after the output of the inverter is stopped, a regenerative current from the motor may be supplied to the DC terminal through the switching device and the inverter, and wherein the controller may control the operating frequency of the motor to be less than or equal to the second frequency during the supply of the regenerative current for the detected DC terminal voltage to be less than or equal to the allowable voltage. Accordingly, burnout of the switching device for switching connection of the motor windings may be prevented, as well as burnout of the inverter. 
     Meanwhile, in response to the windings of the motor being switched from the second connection to the first connection, the controller may control the operating frequency of the motor to decrease to the second frequency or less for the switching element in the brake chopper circuit not to be turned on. Accordingly, it is possible to control the brake chopper circuit at the DC terminal not to operate during the operation of the switching device. As a result, burnout of the switching device for switching connection of the motor windings may be prevented. 
     Meanwhile, in response to the windings of the motor being switched from the second connection to the first connection, the controller may control an output of the inverter to be stopped, and may control a third regenerative current from the motor to be supplied to the DC terminal, and then a fourth regenerative current, which is lower than the third regenerative current, to be supplied to the DC terminal for the switching element in the brake chopper circuit not to be turned on that after the output of the inverter is stopped. Accordingly, it is possible to control the brake chopper circuit at the DC terminal not to operate during the operation of the switching device. As a result, burnout of the switching device for switching connection of the motor windings may be prevented. 
     Meanwhile, the controller may control an operating frequency range of the motor, during switching of the windings of the motor from the first connection to the second connection, to be greater than an operating frequency range of the motor during switching of the windings of the motor from the second connection to the first connection. Accordingly, burnout of the switching device for switching connection of the motor windings may be prevented, as well as burnout of the inverter. 
     Meanwhile, in response to the windings of the motor being switched from the first connection to the second connection, the controller may control the operating frequency of the motor to be greater than or equal to a first reference frequency, and in response to the windings of the motor being switched from the second connection to the first connection, the controller may control the operating frequency of the motor to be greater than or equal to a second reference frequency. Accordingly, burnout of the switching device for switching connection of the motor windings may be prevented, as well as burnout of the inverter. 
     Meanwhile, the motor driving apparatus and the air conditioner including the same according to an embodiment of the present disclosure may further include a temperature detector attached to the inverter and configured to detect temperature of the inverter, wherein in response to the windings of the motor being switched from the first connection to the second connection, the controller may control the temperature of the inverter to be less than or equal to the first reference temperature, and in response to the windings of the motor being switched from the second connection to the first connection, the controller may control the temperature of the inverter to be less than or equal to the second reference temperature which is higher than the first reference temperature. Accordingly, burnout of the switching device for switching connection of the motor windings may be prevented, as well as burnout of the inverter. 
     In order to achieve the above objects, a motor driving apparatus and an air conditioner according to another embodiment of the present disclosure may include: an inverter having a plurality of switching elements, and configured to output alternating current (AC) power to a motor based on a switching operation; a temperature detector attached to the inverter, and configured to detect temperature of the inverter; a switching device disposed between the inverter and the motor, and configured to switch windings of the motor to a first connection or a second connection; and a controller configured to control the inverter and the switching device, wherein in response to the windings of the motor being switched from the first connection to the second connection, the controller may control the temperature of the inverter to be less than or equal to a first reference temperature, and in response to the windings of the motor being switched from the second connection to the first connection, the controller may control the temperature of the inverter to be less than or equal to a second reference temperature which is higher than the first reference temperature. Accordingly, burnout of the switching device for switching connection of the motor windings may be prevented, as well as burnout of the inverter. 
     Meanwhile, the motor driving apparatus and the air conditioner including the same according to another embodiment of the present disclosure may further include: a DC terminal capacitor configured to store a DC terminal voltage; a DC terminal voltage detector configured to detect the DC terminal voltage; and a brake chopper circuit connected to both ends of the DC terminal capacitor and having a resistor and a switching element, wherein in response to the windings of the motor being switched from the second connection to the first connection, the controller controls the temperature of the inverter to be less than or equal to the second reference temperature for the detected DC terminal voltage to be less than or equal to an allowable voltage. Accordingly, it is possible to control the brake chopper circuit at the DC terminal not to operate during the operation of the switching device. As a result, burnout of the switching device for switching connection of the motor windings may be prevented. 
     Meanwhile, in response to the windings of the motor being switched from the first connection to the second connection, the controller may control an output of the inverter to be stopped, and wherein after the output of the inverter is stopped, a regenerative current from the motor may be supplied to the DC terminal through the switching device and the inverter, and wherein the controller may control the temperature of the inverter to be less than or equal to the second reference temperature during the supply of the regenerative current, the detected DC terminal voltage may be less than or equal to the allowable voltage. Accordingly, burnout of the switching device for switching connection of the motor windings may be prevented, as well as burnout of the inverter. 
     Meanwhile, in response to the windings of the motor being switched from the first connection to the second connection, the controller may control the temperature of the inverter to decrease to the first reference temperature or less for the switching element in the brake chopper circuit not to be turned on. Accordingly, burnout of the switching device for switching connection of the motor windings may be prevented, as well as burnout of the inverter. 
     Meanwhile, in response to the windings of the motor being switched from the first connection to the second connection, the controller may control an output of the inverter to be stopped, and may control a first regenerative current from the motor to be supplied to the DC terminal, and then a second regenerative current, which is lower than the first regenerative current, to be supplied to the DC terminal for the switching element in the brake chopper circuit not to be turned on that after the output of the inverter is stopped. Accordingly, it is possible to control the brake chopper circuit at the DC terminal not to operate during the operation of the switching device. As a result, burnout of the switching device for switching connection of the motor windings may be prevented. 
     Meanwhile, in response to the windings of the motor being switched from the second connection to the first connection, the controller may control the temperature of the inverter to be less than or equal to the second reference temperature for the detected DC terminal voltage to be less than or equal to the allowable voltage. Accordingly, burnout of the switching device for switching connection of the motor windings may be prevented, as well as burnout of the inverter. 
     Meanwhile, in response to the windings of the motor being switched from the second connection to the first connection, the controller may control an output of the inverter to be stopped, and wherein after the output of the inverter is stopped, a regenerative current from the motor may be supplied to the DC terminal through the switching device and the inverter, and wherein the controller may control the temperature of the inverter to be less than or equal to the second reference temperature during the supply of the regenerative current for the detected DC terminal voltage to be less than or equal to the allowable voltage. Accordingly, burnout of the switching device for switching connection of the motor windings may be prevented, as well as burnout of the inverter. 
     Meanwhile, in response to the windings of the motor being switched from the second connection to the first connection, the controller may control the temperature of the inverter to decrease to the second reference temperature or less for the switching element in the brake chopper circuit not to be turned on. Accordingly, it is possible to control the brake chopper circuit at the DC terminal not to operate during the operation of the switching device. As a result, burnout of the switching device for switching connection of the motor windings may be prevented. 
     Meanwhile, in response to the windings of the motor being switched from the second connection to the first connection, the controller may control an output of the inverter to be stopped, and may control a third regenerative current from the motor to be supplied to the DC terminal, and then a fourth regenerative current, which is lower than the third regenerative current, to be supplied to the DC terminal for the switching element in the brake chopper circuit not to be turned on that after the output of the inverter is stopped. Accordingly, it is possible to control the brake chopper circuit at the DC terminal not to operate during the operation of the switching device. As a result, burnout of the switching device for switching connection of the motor windings may be prevented. 
     Meanwhile, an operating method of the motor driving apparatus and the air conditioner according to the present disclosure can be realized as a processor-readable code written on a recording medium readable by a processor included in the motor driving apparatus and the air conditioner. The processor-readable recording medium may be any type of recording device in which data is stored in a processor-readable manner. Examples of the processor-readable recording medium include a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disc, an optical data storage, and a carrier wave, e.g., data transmission through the Internet. The processor-readable recording medium can be distributed over a plurality of computer systems connected to a network so that a processor-readable code is written thereto and executed therefrom in a decentralized manner. 
     It will be apparent that, although the preferred embodiments have been shown and described above, the present disclosure is not limited to the above-described specific embodiments, and various modifications and variations can be made by those skilled in the art without departing from the gist of the appended claims. Thus, it is intended that the modifications and variations should not be understood independently of the technical spirit or prospect of the present disclosure.