KR20100106824A - Apparatus for dirving motor of air conditioner - Google Patents

Abstract

PURPOSE: A device for driving a motor of an air conditioning device is provided to enhance the stability of a circuit in a driving device since a motor stops if the calculated input voltage is beyond an allowable range. CONSTITUTION: A device for driving a motor of an air conditioning device comprises a converter(210), an input voltage detection part(A), an inverter(220), an output current detection unit(E), and a controller(230). The converter changes the input AC power into the DC power. The input voltage detection part detects the input voltage from the input AC power. The inverter includes a plurality of switching elements, changes the DC power into the AC power of a fixed frequency by a switching operation and drives a motor(250). The output current detection unit detects the output current flowing between the inverter and the motor. The controller estimates the input current from the input AC power based on the detected output current and the detected input voltage.

Description

Apparatus for dirving motor of air conditioner

The present invention relates to an electric motor driving apparatus of an air conditioner, and more particularly, to an electric motor driving apparatus of an air conditioner capable of simply calculating the input voltage of the electric motor driving apparatus.

An air conditioner is a device that is disposed in a room, a living room, an office, or a business store to adjust a temperature, humidity, cleanliness, and airflow of an air to maintain a comfortable indoor environment.

Air conditioners are generally divided into one-piece and separate types. The integrated type and the separate type are functionally the same, but the integrated type integrates the functions of cooling and heat dissipation to install a hole in the wall of the house or hang the device on the window. On the side, an outdoor unit that performs heat dissipation and compression functions was installed, and two separate devices were connected by refrigerant pipes.

In the air conditioner, an electric motor is used for a compressor, a fan, and the like, and an electric motor driving device for driving the air conditioner is used. The motor driving device receives a commercial AC power, converts the DC voltage into a DC voltage, converts the DC voltage into a commercial AC power having a predetermined frequency, and supplies the same to the motor, thereby controlling the motor to drive a motor such as a compressor or a fan.

An object of the present invention is to provide an electric motor driving apparatus of an air conditioner that can simply calculate an input voltage of the electric motor driving apparatus.

The motor driving apparatus of the air conditioner according to the embodiment of the present invention for solving the above-mentioned problems and other problems is a converter for converting the input AC power source to the DC power source, and an input for detecting the input current from the input AC power source An inverter including a current detector, a plurality of switching elements, and converting a direct current power source into an alternating current power source of a predetermined frequency by a switching operation to drive an electric motor, an output current detection unit detecting an output current flowing between the inverter and the motor; And a controller for estimating an input voltage from the input AC power source based on the detected output current and the detected input current.

As described above, the motor driving apparatus of the air conditioner according to the embodiment of the present invention can simply calculate the input voltage based on the detected input current and the detected output current.

In addition, when the calculated input voltage exceeds the allowable range, by stopping the output of the inverter switching control signal to stop the operation of the motor, the stability of the circuit elements in the driving apparatus is improved.

In addition, when the calculated input voltage exceeds the allowable range, the output of the converter switching control signal is stopped, whereby the stability of the circuit elements in the driving apparatus is further improved.

In addition, the control unit can control the converter and the inverter at the same time, it is possible to efficiently control the drive device.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic diagram of an air conditioner according to the present invention.

Referring to the drawings, the air conditioner 50 is largely divided into an indoor unit (I) and an outdoor unit (O).

The outdoor unit O includes a compressor 2 serving to compress the refrigerant, a compressor electric motor 2b for driving the compressor, an outdoor side heat exchanger 4 serving to radiate the compressed refrigerant, and an outdoor unit. An outdoor blower 5 disposed on one side of the heat exchanger 4 and including an outdoor fan 5a for promoting heat dissipation of the refrigerant and an electric motor 5b for rotating the outdoor fan 5a, and an expansion for expanding the condensed refrigerant; The mechanism 6, the cooling / heating switching valve 10 for changing the flow path of the compressed refrigerant, and the accumulator 3 for temporarily storing the gasified refrigerant to remove moisture and foreign matter and then supplying a refrigerant of a constant pressure to the compressor. And the like.

The indoor unit (I) is disposed inside the indoor heat exchanger (8) performing cooling / heating functions, and the indoor fan (9a) and the indoor disposed at one side of the indoor heat exchanger (8) to promote heat dissipation of the refrigerant. And an indoor blower 9 made of an electric motor 9b for rotating the fan 9a.

At least one indoor side heat exchanger (8) may be installed. The compressor 2 may be at least one of an inverter compressor and a constant speed compressor.

In addition, the air conditioner 50 may be configured as a cooler for cooling the room, or may be configured as a heat pump for cooling or heating the room.

On the other hand, the motor in the motor drive device of the air conditioner according to an embodiment of the present invention can be each of the motor (2b, 5b, 9b) to operate the outdoor fan, compressor or indoor fan of the air conditioner, shown in the figure have.

Meanwhile, although FIG. 1 illustrates one indoor unit (I) and one outdoor unit (O), the driving device of the air conditioner according to the embodiment of the present invention is not limited thereto, and includes a plurality of indoor units and outdoor units. Applicable to the air conditioner, an air conditioner having a single indoor unit and a plurality of outdoor units, of course.

2 is a circuit diagram illustrating a motor driving apparatus of an air conditioner according to an embodiment of the present invention.

Referring to the drawings, according to an embodiment of the present invention, the motor driving apparatus 200 of FIG. 2 includes a converter 210, an inverter 220, a controller 230, an input current detector A, and an output current. The detection unit E is included. In addition, the motor driving apparatus 200 of FIG. 2 may further include a reactor L, a smoothing capacitor C, a dc terminal voltage detector B, and the like.

The reactor L is disposed between the commercial AC power supply 205 and the converter 210 to perform power factor correction or step-up operation. In addition, the reactor L may perform a function of limiting harmonic currents due to the fast switching of the converter 210.

The input current detector A may detect an input current i _s input from the commercial AC power supply 205. To this end, a current sensor, CT (current trnasformer), shunt resistor, or the like can be used. The detected input current i _s is a discrete signal in the form of a pulse and may be input to the controller 230 for estimation of the input voltage v _s and generation of the converter switching control signal Scc. have.

The converter 210 converts the commercial AC power source 205 passed through the reactor L into a DC power source and outputs the DC power source. Although the commercial AC power supply 205 is shown as a single phase AC power supply in the figure, it may be a three phase AC power supply. The internal structure of the converter 210 also varies according to the type of the commercial AC power source 205. For example, in the case of a single phase AC power supply, a half bridge type converter in which two switching elements and four diodes are connected may be used, and in the case of a three phase AC power supply, six switching elements and six diodes may be used.

The converter 210 includes a switching element and performs a boosting operation, a power factor improvement, and a DC power conversion by a switching operation. On the other hand, the converter 210 may be made of a diode or the like to perform rectification without a separate switching operation.

The smoothing capacitor C is connected to the output terminal of the converter 210. The converted DC power output from the converter 210 is smoothed. Hereinafter, the output terminal of the converter 210 is referred to as a dc terminal or a dc link terminal. The DC voltage smoothed at the dc stage is applied to the inverter 220.

The dc end voltage detector B may detect a dc end voltage Vdc that is both ends of the smoothing 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 is detected, and the detected dc terminal voltage Vdc is a discrete signal in the form of a pulse, which estimates the input voltage v _s and generates the converter switching control signal Scc. For example, the control unit 230 may be input to the controller 230.

The inverter 220 includes a plurality of inverter switching elements, converts a smoothed DC power source into a three-phase AC power source having a predetermined frequency by on / off operation of the switching element, and outputs the same to the three-phase electric motor 250.

Inverter 220 is a pair of upper arm switching elements (Sa, Sb, Sc) and lower arm switching elements (S'a, S'b, S'c) connected in series with each other, a total of three pairs of upper and lower arms The switching elements are connected in parallel with each other (Sa & S'a, Sb & S'b, Sc & S'c). Diodes are connected in anti-parallel to each of the switching elements Sa, S'a, Sb, S'b, Sc, and S'c.

The switching elements in the inverter 220 perform on / off operations of the respective switching elements based on the inverter switching control signal Sic from the controller 230. As a result, the three-phase AC power supply having the predetermined frequency is output to the three-phase electric motor 250.

The output current detector E detects the output current i _o flowing between the inverter 220 and the three-phase motor 250. In other words, the current flowing through the motor 250 is detected. The output current detector E may detect the output current of each phase, or may detect the output current of one or two phases by using three-phase equilibrium.

The output current detector E may be located between the inverter 220 and the motor 250, and a current sensor, a current trnasformer (CT), a shunt resistor, or the like may be used for current detection. For example, one end of the shunt resistor may be connected to three lower arm switching elements S'a, S'b, and S'c of the inverter 220, respectively.

The detected output current i _o , as a discrete signal in the form of a pulse, may be applied to the controller 230, and based on the detected output current i _o , to estimate the input current. Can be used. In addition, the detected output current i _o may be used to generate the inverter switching control signal Sic.

The controller 230 estimates the input voltage v _s based on the detected output current i _o and the detected input current i _s . For example, when the detected output current i _o is a current flowing in one of three phases of the motor, the motor output power P _M consumed in the motor 250 is calculated using the same, and the detected input After calculating the input power consumption P _i using the current i _s , the input voltage v _s can be estimated by comparing the motor power consumption P _M with the input power consumption _Pi . have. That is, since the input power consumption _Pi and the motor power consumption P _M are approximately equal, the input voltage v _s is estimated using this. This will be described in detail with reference to FIG. 3 to be described later.

The above-described method for estimating the input voltage v _s is based on the premise that the motor 250 operates and the output current i _o flows to the motor 250.

When the motor 250 is stopped, the method of estimating the input voltage v _s may be different from that described above. In this case, the controller 230 estimates the input voltage v _s based on the detected dc terminal voltage Vdc. For example, when the motor 250 is in a stopped state, the input voltage v _s can be estimated by using the voltage equation from the commercial AC power supply 205 to the dc terminal. It describes in detail with reference.

On the other hand, the above-described method of estimating the input voltage (v _s ) according to the operation or stop state of the motor 250 may be applied to a compressor motor, but is not limited to this may be applied to a variety of fan motors. .

Meanwhile, the controller 230 may perform an overvoltage protection operation based on the estimated magnitude of the input voltage v _'s . This will be described later with reference to FIG. 3.

On the other hand, the control unit 230 controls the switching operation of the inverter 230. To this end, the controller 230 receives the output current i _o detected by the output current detector E, generates an inverter switching control signal Sic, and outputs it to the inverter 220. The inverter switching control signal Sic may be a switching control signal for pulse width modulation (PWM). A detailed operation of the output of the inverter switching control signal Sic in the controller 230 will be described later with reference to FIG. 3.

The controller 230 may also control a switching operation of the converter 210. To this end, the controller 230 receives the dc terminal voltage Vdc detected by the dc terminal voltage detection unit B, generates a converter switching control signal Scc, and outputs it to the converter 210. The converter switching control signal Scc may be a switching control signal for PWM. A detailed operation of the output of the converter switching control signal Scc in the controller 230 will be described later with reference to FIG. 5.

Three-phase electric motor 250 is provided with a stator and a rotor, each phase AC power of a predetermined frequency is applied to the coil of each stator, the rotor is rotated. The type of the motor 250 may be a variety of forms, such as a brushless DC (BLDC) motor, a synchronous reluctance motor (synRM).

The three-phase electric motor 250 may be used as a fan motor or a compressor motor in an outdoor unit of an air conditioner, and may also be used as a fan motor in an indoor unit of an air conditioner.

On the other hand, when the driving device 200 of the air conditioner described above, for example, for driving a fan motor or a compressor motor used in the outdoor unit, the control unit 230 as an outdoor unit control unit, can be disposed separately in the indoor unit. It is also possible to perform further communication with the indoor unit controller. The outdoor unit control unit receives a driving command by communication with the indoor unit control unit, and can determine a speed command value to be described later based on the received driving command.

In addition, the controller 230 of the driving apparatus 200 of the air conditioner described above may control the fan motor and the compressor motor used in the outdoor unit at the same time.

3 is a simplified block diagram of the inside of the controller of FIG. 2.

Referring to the drawings, the controller 230 includes an input voltage estimator 340 and an abnormality determiner 350. The controller 230 further includes a speed estimator 305, a current command generator 310, a voltage command generator 320, and a switching control signal output unit 330.

On the other hand, although not shown in the drawings, the three-phase output current (i _o ) may be further included an axis conversion unit for converting the d-axis, q-axis current or the d-axis, q-axis current to three-phase current.

The speed estimating unit 305 estimates the speed v of the electric motor based on the detected output current i _o . It is also possible to estimate the position of the rotor. For example, the mechanical equations of the electric motor 250 and the electric equations can be compared with each other to estimate the speed v of the electric motor accordingly.

The current command generation unit 310 generates the current command values i ^* _d , i ^* _q based on the estimated speed v and the speed command value v ^* . For example, the current command generation unit 310 may generate a current command value i ^* _d , i ^* _q by performing PI control based on the difference between the estimated speed v and the speed command value v ^* . Can be. To this end, the current command generation unit 310 may be provided with a PI controller (not shown). Further, a limiter (not shown) may be further provided to limit the level so that the current command value i ^* _d , i ^* _q does not exceed the allowable range.

The voltage command generation unit 320 generates the voltage command value v ^* _d , v ^* _q based on the detected output current i _o and the calculated current command value i ^* _d , i ^* _q . For example, the voltage command generation unit 320 performs PI control based on the difference between the detected output current i _o and the calculated current command value i ^* _d , i ^* _q to perform the voltage command value v. ^* _d , v ^* _q ) To this end, the voltage command generation unit 320 may include a PI controller (not shown). Further, a limiter (not shown) may be further provided to limit the level so that the voltage command value v ^* _d , v ^* _q does not exceed the allowable range.

The switching control signal output unit 330 generates an inverter switching control signal Sic, which is a PWM signal, based on the voltage command values v ^* _d and v ^* _q and outputs the same to the inverter 220. Accordingly, the switching elements Sa, S'a, Sb, S'b, Sc, and S'c in the inverter 220 perform an on / off switching operation.

The input voltage estimating unit 340 is connected to the input current i _s detected from the input current detector A and the output current i _o detected from the output current detector E during the operation of the motor 250. On the basis of this, the input voltage v _s is estimated, and when the motor 250 is stopped, the input voltage v _s is estimated on the basis of the dc end voltage Vdc detected from the dc end voltage detector B. .

First, the input voltage v _s during the operation of the motor 250 will be described with reference to the estimating method, and the input voltage estimating unit 340 is the motor power consumption P _M and the input power consumption Pi due to the input power P _i. ), And estimate the input voltage. The power consumption flowing in each phase of the three-phase electric motor 250 is determined by the output current i _o , the output voltage v _o , and the power factor pf between the output current i _o and the output voltage. As a result, the electric power consumption (P _M ) consumed in the three-phase electric motor as shown in Equation 1 below.

Here, the output voltage v _o and the power factor pf can also be calculated based on the output current i _o . For example, it can be obtained by the mechanical equation and the electric equation of the electric motor 250.

On the other hand, the input power consumption (P _i ) is determined by the input current (i _s ) and the input voltage (i _s ), therefore, the estimated input voltage (v ' _s ), the electric power consumption of the motor according to equation (1) It is determined by (P _M ) and the detected input current (i _s ) as shown in Equation 2 below.

As described above, the input voltage estimating unit 340 based on the detected input current i _s and the detected output current i _o according to Equations 1 and 2, input voltage v ' _s ) can be easily estimated. The estimated input voltage v ' _s is input to the abnormality determination unit 350.

On the other hand, the input voltage estimator 340 also calculates a phase θ _M between the input voltage and the input current based on the detected input current i _s and the estimated input voltage v ' _s . It is possible. The calculated phase can also be used in FIG. 6 described later.

Next, the method for estimating the input voltage v _s at the time of stopping the motor 250 will be described. The input voltage estimating unit 340 calculates the input voltage v _s based on the detected dc terminal voltage Vdc. Estimate. When the motor 250 is in the stopped state, the input voltage v _s can be estimated by the voltage equation from the commercial AC power source 205 to the dc terminal. That is, the input voltage v _s may be obtained as a difference between the detected dc terminal voltage Vdc and the voltage Vth consumed by the circuit element in the converter 210. This is shown in Equation 3 below.

When a circuit element in the converter 210 is formed of a diode, the voltage Vth consumed by the circuit element in the converter 210 may be an operating voltage (threshold voltage) of the diode. When the circuit elements in the converter 210 are composed of diodes and switching elements, the voltage Vth consumed by the circuit elements in the converter 210 may be the sum of operating voltages (threshold voltages) of the diodes and the switching elements.

The abnormality determination unit 350 determines whether the overvoltage is based on the estimated estimated input voltage v ' _s . For example, when exceeding a preset allowable value as one cycle average value or rms value of the estimated magnitude of the input voltage v _'s , the abnormality determination unit 350 determines that it is an overvoltage and determines the switching control signal output unit 330. Outputs an operation stop signal Sst.

 When the switching control signal output unit 330 receives the operation stop signal Sst, the switching control signal output unit 330 stops output of the inverter switching control signal Sic. Accordingly, burnout of the circuit elements in the driving apparatus 200 may be prevented, and thus the safety of the circuit elements may be secured.

4 is a circuit diagram illustrating an example of the converter of FIG. 2.

Referring to the drawings, the converter 210 includes four diode elements D1 to D4.

For rectifying operation of the converter 210, four diode elements D1 to D4 are arranged in a bridge form in a single-phase commercial AC power supply. That is, the third and fourth diode elements D1 to D2 are connected in series with each other, and the third and fourth diode elements D3 to D4 are connected in series with each other and are connected in series with each other. The diode elements D3 to D4 are connected in parallel with the first and second diode elements D1 to D2.

Briefly, the operation of the single-phase commercial AC power supply is positive, and the rectifying operation is performed through the first and fourth diodes D1 and D4, and when the single-phase commercial AC power supply is the negative polarity, the second and third diodes. The rectification operation is performed through (D2, D3).

Meanwhile, the voltage Vth consumed by the circuit element in the converter 210 described above may be approximately 2V as a sum of operating voltages (threshold voltages) of the two diode elements D1, D4, D2, and D3.

5 is a circuit diagram illustrating another example of the converter of FIG. 2.

Referring to the drawings, the converter 210 includes four diode elements D11 to D14 and two switching elements S1 to S2.

For rectifying operation of the converter 210, four diode elements D11 to D14 are arranged in a bridge form in a single-phase commercial AC power supply. That is, the third and fourth diodes D11 to D12 are connected to each other in series, and the third and fourth diode elements D13 to D14 are connected to each other in series and connected to each other in series. The diode elements D13 to D14 are connected in parallel with the first and second diode elements D11 to D12. Among the lower two diode elements D12 and D14, switching elements S1 to S2 are connected in parallel, respectively.

Briefly describing the operation, the current component is stored in the reactor L by the turn-on operation of the switching element S1 or S2 and stored in the reactor L by the turn-off operation of the switching element S1 or S2. The current component is stored in the smoothing capacitor (C). Thereby, the boosting function is performed, and the power factor correction can be performed by the on / off switching time.

Meanwhile, the voltage Vth consumed by the circuit element in the converter 210 described above may be approximately 2V as a sum of operating voltages (threshold voltages) of the two diode elements and the switching element.

6 is a simplified block diagram of the inside of the control unit of FIG. 2.

Referring to the drawings, the controller 230, the converter current command generation unit 610, the duty generation unit 620, and the converter switching control signal output unit 630 to generate the converter switching control signal Scc. ) May be further included. This assumes that the converter 210 includes a switching element, as shown in FIG. 5.

The converter current command generation unit 610 generates a current command value I ^* based on the detected dc terminal voltage Vdc and the dc voltage command value V ^* dc. For example, the converter current command generation unit 610 generates a current command value I ^* by performing PI control based on a difference between the detected dc terminal voltage Vdc and the dc voltage command value V ^* dc. can do. To this end, the converter current command generation unit 610 may include a PI controller (not shown). In addition, a limiter (not shown) may be further provided to limit the level so that the current command value I ^* does not exceed the allowable range.

On the other hand, the duty generator 620 based on the current command value I ^* , the detected input current i _s , and the estimated input voltage v ' _s from the converter current command generator 510, The duty d of the switching element S1 or S2 in the converter 210 is calculated. For example, the duty generator 620 may calculate the phase θ _M based on the detected input current i _s and the estimated input voltage v _s .

The duty generator 620 may be configured such that the value of I ^* cosθ _M and the detected input current are determined by the phase θ _M and the current command value I ^* calculated by the input voltage estimator 340 or the duty generator 620. Based on the difference of i _s ), P control may be performed to generate the duty d. To this end, the duty generator 620 may include a P controller (not shown).

The converter switching control signal output unit 630 generates a switching control signal Scc, which is a PWM signal, based on the generated duty d and outputs the converted control signal Scc to the converter 210. Accordingly, the switching element S1 or S2 in the converter 210 performs an on / off switching operation.

On the other hand, when the converter switching control signal output unit 630 receives the operation stop signal Sst, the converter switching control signal Scc stops outputting the converter switching control signal Scc. Accordingly, burnout of the circuit elements in the driving apparatus 200 may be prevented, and thus the safety of the circuit elements may be secured.

7 is a flowchart illustrating a method of estimating an input voltage according to an embodiment of the present invention.

Referring to the drawings, the control unit 230 determines whether the electric motor 250 is operating (S710). This may be determined by whether the output current i _o detected by the output current detector E has a predetermined value equal to or greater than zero.

Next, when it is determined that the motor 250 is stopped, the dc terminal voltage detector B detects the dc terminal voltage Vdc (S720), and the controller 230 based on the detected dc terminal voltage Vdc. By estimating the input voltage (S730). The controller 230 estimates the input voltage by calculating a difference between the detected dc terminal voltage Vdc and the voltage Vth consumed by the circuit elements in the converter 210 as in Equation 3 described above.

Next, when it is determined that the motor 250 is in operation, the output current detector E and the input current detector A detect the output current i _o and the input current i _s , respectively (S725). 230 estimates an input voltage based on the detected output current i _o and the input current i _s (S735). The controller 230 estimates the input voltage based on the motor power consumption P _M and the detected input current i _s as in Equations 1 and 2 described above.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be understood that the invention may be practiced. Therefore, the embodiments described above are to be understood as illustrative and not restrictive in all aspects. In addition, the scope of the present invention is shown by the claims below, rather than the above detailed description. Also, it is to be construed that all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts are included in the scope of the present invention.

1 is a schematic diagram of an air conditioner according to the present invention.

2 is a circuit diagram illustrating a motor driving apparatus according to an embodiment of the present invention.

3 is a simplified block diagram of the inside of the controller of FIG. 2.

4 is a circuit diagram illustrating an example of the converter of FIG. 2.

5 is a circuit diagram illustrating another example of the converter of FIG. 2.

6 is a simplified block diagram of the inside of the control unit of FIG. 2.

7 is a flowchart illustrating a method of estimating an input voltage according to an embodiment of the present invention.

<Explanation of symbols on main parts of the drawings>

210: converter 220: inverter

230: controller 310: speed estimation unit

310: current command generator 320: voltage command generator

330: switching control signal output unit 340: input voltage estimation unit

350: abnormality determination unit A: input current detection unit

B: DC stage voltage detector E: Output current detector

Claims (11)

A converter for converting input AC power into DC power; An input current detector for detecting an input current from the input AC power source; An inverter having a plurality of switching elements and converting the DC power into AC power of a predetermined frequency by a switching operation to drive an electric motor; An output current detector for detecting an output current flowing between the inverter and the motor; And And a control unit for estimating an input voltage from the input AC power source based on the detected output current and the detected input current. The method of claim 1, The control unit, And an electric motor driving device of the air conditioner, wherein the input voltage from the input AC power source is estimated based on the detected output current and the detected input current during the motor operation. The method of claim 1, And a dc end voltage detector configured to detect a dc end voltage which is an output end of the converter. And the control unit estimates the input voltage on the basis of the detected dc terminal voltage when the motor is stopped. The method of claim 1, The control unit, And comparing the motor power consumption based on the detected output current with the input power consumption based on the detected input current to estimate the input voltage. The method of claim 1, The control unit, And an input voltage estimator for estimating the input current based on the detected output current and the detected input current. The method of claim 1, The control unit, And an inverter switching control signal for driving the switching element of the inverter based on the detected output current. The method of claim 6, The control unit, And an abnormality determining unit determining whether an overvoltage is detected based on the estimated magnitude of the input voltage. And stopping the output of the inverter switching control signal when the overvoltage is judged. The method of claim 6, The control unit, A speed estimating unit estimating a speed of the electric motor based on the detected output current; A current command generation unit that generates a current command value based on the estimated speed and the speed command value; A voltage command generator for generating a voltage command value based on the current command value and the detected output current; And And a switching control signal output unit configured to generate and output the inverter switching control signal based on the voltage command value. The method of claim 1, And a dc end voltage detector configured to detect a dc end voltage which is an output end of the converter. The control unit, And outputting a converter switching control signal for driving the switching element of the converter based on the detected dc terminal voltage and the detected input current. 10. The method of claim 9, The control unit, And the output of the converter switching control signal is stopped when the estimated input voltage exceeds the allowable range. 10. The method of claim 9, The control unit, A converter current command generation unit that generates a current command value based on the detected dc end voltage and dc end voltage command value; A duty generator configured to generate a duty based on the current command value and the detected input current; And And a converter switching control signal output unit configured to generate and output the converter switching control signal based on the generated duty.

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