Apparatus for driving an electric motor using a virtual sensor signal and method therefor

Abstract

A method for driving an electric motor includes the steps of: a voltage detection unit detecting a terminal voltage for one of the three phases of the electric motor with respect to a voltage input from an inverter by converting it into a voltage divided magnitude through a resistor connected in parallel to the input terminal; a position derivation unit deriving a first rotor position signal simulating a Hall sensor signal of one of three Hall sensors virtually mounted on the electric motor based on the terminal voltage; and a position estimation unit deriving a second rotor position signal and a third rotor position signal simulating the remaining two Hall sensor signals of the three Hall sensors based on the first rotor position signal.

Description

Technology Field

[0001] The present invention relates to electric motor driving, and more specifically, to an apparatus for driving an electric motor based on a virtual sensor signal and a method for the same. Background Technology

[0002] Brushless Direct Current (BLDC) motors require rotor position detection sensors, such as Hall sensors or encoders, because the phase current of the motor must be switched according to the rotor position. However, the attachment of position sensors causes many problems, including increased motor system costs, increased volume, reduced reliability, limitations on the operating environment, and electromagnetic interference. In particular, the increase in motor costs due to the attachment of sensors acts as the biggest obstacle to the market expansion of BLDC motors. Accordingly, the development of sensorless drive systems that operate BLDC motors without position sensors has recently attracted significant attention, and active research is underway to apply this to applications requiring variable speed operation, replacing existing induction or DC motors. Prior art literature

[0003] Korean Patent Publication No. 2023-0024430 (Published on February 20, 2023) The problem to be solved

[0004] The objective of the present invention is to provide an apparatus for driving an electric motor using a virtual sensor signal and a method for doing the same. means of solving the problem

[0005] A method for driving a motor according to a preferred embodiment of the present invention for achieving the purpose described above comprises: a voltage detection unit detecting a terminal voltage for one of the three phases of the motor with respect to a voltage input from an inverter by converting it into a voltage divided magnitude through a resistor connected in parallel to the input terminal; a position derivation unit deriving a first rotor position signal simulating a Hall sensor signal of one of three Hall sensors virtually mounted on the motor based on the terminal voltage; and a position estimation unit deriving a second rotor position signal and a third rotor position signal simulating the remaining two Hall sensor signals of the three Hall sensors based on the first rotor position signal.

[0006] The step of deriving the first rotor position signal includes the step of deriving a first ground voltage having a sinusoidal wave that is 90 degrees grounded through filtering of the divided terminal voltage by an active filter, and the step of deriving the first rotor position signal by an integrator and a zero-point detection circuit grounding the first ground voltage by 90 degrees and detecting a zero point.

[0007] The step of deriving the second rotor position signal and the third rotor position signal comprises: a step in which a PLL circuit performs a 6x multiplication on the first rotor position signal to generate a 6x multiplication signal; a step in which a binary counter rectifies the 6x multiplication signal to generate a rectified signal; a step in which a first Johnson counter derives a plurality of state signals shifted in units of the period of the rectified signal from the rectified signal; a step in which a second Johnson counter derives a plurality of inverted state signals in units of the period of the rectified signal from the inverted signal of the rectified signal; and a step in which a logic circuit derives the second rotor position signal and the third rotor position signal using at least some of the plurality of state signals and the plurality of inverted state signals.

[0008] The above method further comprises the steps of: a control unit detecting a sector number in which a rotor is located in a plurality of sectors in which a complex space is divided by six boundary voltage vectors from a combination signal which is a combination of the first rotor position signal, the second rotor position signal, and the third rotor position signal; the control unit calculating an angle of the rotor based on the combination signal and the sector number; the control unit deriving a time for applying a first boundary voltage vector and a time for applying a second boundary voltage vector of the corresponding sector from the sector number and the angle of the rotor; the control unit generating a control signal for controlling a switch of the inverter based on the time for applying the first boundary voltage vector and the time for applying the second boundary voltage vector; and the control unit controlling a plurality of switches of the inverter according to the control signal.

[0009] The step of calculating the angle of the rotor above is performed by a control unit

[0010] mathematical formula

[0011]

[0012] The angle of the rotor is calculated according to the above, wherein θ is the angle of the rotor and STRN is a sector number in complex space.

[0013] The step of generating the above control signal is performed by a control unit

[0014] mathematical formula

[0015]

[0016]

[0017] According to the above, the time for applying the first boundary voltage vector and the time for applying the second boundary voltage vector of the corresponding sector are derived from the sector number and the angle of the rotor, wherein T1 is the time for applying the first boundary voltage vector, T2 is the time for applying the second boundary voltage vector, Ts is the sampling time, V* is the command voltage, θ is the electrical angle of the rotor, and Vdc is the DC power supply voltage.

[0018] A device for driving a motor according to a preferred embodiment of the present invention for achieving the purpose described above includes a voltage detection unit that detects a terminal voltage for one of the three phases of the motor with respect to a voltage input from an inverter by converting it into a voltage divided magnitude through a resistor connected in parallel to the input terminal; a position derivation unit that derives a first rotor position signal simulating a Hall sensor signal of one of three Hall sensors virtually mounted on the motor based on the terminal voltage; and a position estimation unit that derives a second rotor position signal and a third rotor position signal simulating the remaining two Hall sensor signals of the three Hall sensors based on the first rotor position signal.

[0019] The above device further includes a control unit that detects a sector number where a rotor is located in a plurality of sectors divided by six boundary voltage vectors in a complex space from a combination signal which is a combination of the first rotor position signal, the second rotor position signal, and the third rotor position signal, calculates the angle of the rotor based on the combination signal and the sector number, derives the time for applying the first boundary voltage vector and the time for applying the second boundary voltage vector of the corresponding sector from the sector number and the angle of the rotor, generates a control signal for controlling the switches of the inverter based on the time for applying the first boundary voltage vector and the time for applying the second boundary voltage vector, and controls the plurality of switches of the inverter according to the control signal. Effects of the invention

[0020] According to the present invention, the angle of the rotor is derived using a sensor signal that simulates a Hall sensor signal, i.e., a virtual sensor signal, and a control signal for spatial vector modulation is generated based on this to control the switches of the inverter, thereby enabling control of the electric motor. Accordingly, stable sensorless operation over a wide speed range is possible at a lower cost than conventional sensorless methods. Brief explanation of the drawing

[0021] FIG. 1 is a diagram illustrating the configuration of a device for driving a motor based on a virtual sensor signal according to an embodiment of the present invention. FIG. 2 is a diagram illustrating the detailed configuration of a position derivation unit for driving a motor based on a virtual sensor signal according to an embodiment of the present invention. FIG. 3 is a diagram illustrating the detailed configuration of a position detection unit for driving a motor based on a virtual sensor signal according to an embodiment of the present invention. FIG. 4 is a flowchart illustrating a method for driving a motor based on a virtual sensor signal according to an embodiment of the present invention. FIG. 5 is a timing diagram for explaining a method for deriving a first rotor position signal according to an embodiment of the present invention. FIGS. 6 and FIGS. 7 are timing diagrams for explaining a method for deriving a second rotor position signal and a third rotor position signal according to an embodiment of the present invention. FIG. 8 is a conceptual diagram illustrating a method for deriving sector numbers of a complex space according to an embodiment of the present invention. FIGS. 9 and FIGS. 10 are conceptual diagrams for explaining a control method based on spatial vector modulation according to an embodiment of the present invention. Specific details for implementing the invention

[0022] Before the detailed description of the present invention, it should be understood that the embodiments described in this specification and the configurations illustrated in the drawings are merely the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention, and that various equivalents and modifications that can replace them may exist at the time of filing this application.

[0023] Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that identical components in the accompanying drawings are indicated by the same reference numerals whenever possible. Furthermore, detailed descriptions of known functions and configurations that could obscure the essence of the invention will be omitted. For the same reason, some components in the accompanying drawings may be exaggerated, omitted, or schematically depicted, and the size of each component does not entirely reflect its actual size.

[0024] In addition, the terms and words used in the specification and claims described below should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0025] First, we will describe a device for driving a motor based on a virtual sensor signal according to an embodiment of the present invention.

[0026] FIG. 1 is a diagram illustrating the configuration of a device for driving a motor based on a virtual sensor signal according to an embodiment of the present invention. FIG. 2 is a diagram illustrating the detailed configuration of a position derivation unit for driving a motor based on a virtual sensor signal according to an embodiment of the present invention. FIG. 3 is a diagram illustrating the detailed configuration of a position detection unit for driving a motor based on a virtual sensor signal according to an embodiment of the present invention.

[0027] Referring to FIG. 1, a device (10, hereinafter abbreviated as 'driving device') for driving a motor based on a virtual sensor signal according to an embodiment of the present invention basically comprises a power supply (SS) for applying a three-phase voltage to supply power to the driving device (10), a rectifier (RCF) for rectifying the voltage supplied from the power supply (SS) to output a pulsating voltage, a smoother (SM) for smoothing the pulsating voltage from the rectifier (RCF) to provide a DC voltage, an inverter (INV) having a plurality of switches for applying the three-phase DC voltage as a driving signal (e.g., a PWM signal), and a motor (MT) driven according to the driving signal.

[0028] Additionally, the driving device (10) further includes a detection unit (100), a position derivation unit (200), a position detection unit (300), and a control unit (400).

[0029] The detection unit (100) is interposed in the input path of one phase (e.g., phase A) of a driving signal (e.g., PWM signal) input from an inverter (INV) to a motor (MT). The detection unit (100) includes a pair of resistors (R1, R2) connected in parallel. The detection unit (100) can detect the terminal voltage (Va) for one of the three phases of the motor (e.g., phase A) with respect to the voltage input from the inverter (INV) by converting it into a divided magnitude through resistors (R1, R2) that are connected in parallel to the input terminal of one of the three phases (e.g., phase A) and have the same resistance value.

[0030] The position derivation unit (200) is intended to derive a first rotor position signal (Ha) that simulates the signal of one of three Hall sensors virtually mounted on the motor (MT) based on the terminal voltage (Va). That is, the three Hall sensors are not actually mounted on the motor (MT), but are assumed to be mounted on the motor (MT). That is, the first rotor position signal (Ha) simulates the signal detected by one of the Hall sensors when it is assumed that three Hall sensors are mounted on the motor (MT).

[0031] To this end, the position finding unit (200), with reference to FIG. 2, includes an active filter (210), an integrator, and a zero-point detection circuit (220).

[0032] The active filter (210) derives a first ground voltage (Va') having a 90-degree grounded sinusoidal wave through filtering the divided terminal voltage (Va) detected by the detector (100).

[0033] The integrator and zero-point detection circuit (220) can derive the first rotor position signal (Ha) by integrating the first ground voltage (Va') to ground the first ground voltage (Va') by 90 degrees (Va'') and detecting the zero point (Vzc).

[0034] The position estimation unit (300) is intended to derive a second rotor position signal (Hb) and a third rotor position signal (Hc) that simulate the signals of the remaining two Hall sensors among the three Hall sensors based on the first rotor position signal (Ha). Similar to the first rotor position signal (Ha), the second rotor position signal (Hb) and the third rotor position signal (Hc) simulate the signals detected by the remaining two Hall sensors, not the Hall sensor corresponding to the first rotor position signal (Ha), when it is assumed that three Hall sensors are virtually mounted on the motor (MT).

[0035] To this end, the position estimation unit (300), with reference to FIG. 3, includes a PLL circuit (310), a binary counter (320), a first Johnson counter (331), a second Johnson counter (332), and a logic circuit (340).

[0036] The PLL circuit (310) is intended to generate a 6x multiplied signal (6X) by performing a 6x multiplier on the first rotor position signal (Ha).

[0037] The binary counter (320) can rectify the 6x multiplied signal (6X) to generate a rectified signal (RTF).

[0038] The first Johnson counter (331) is a rectified signal ( A plurality of state signals (Q0, Q1, Q2) that are shifted in units of the period of the rectified signal are derived from ). Correspondingly, the second Johnson counter (332) is the inverted signal of the rectified signal ( A plurality of inverted state signals (X0, X1, X2) are derived from the rectified signal in cycle units.

[0039] The logic circuit (340) is intended to derive a second rotor position signal (Hb) and a third rotor position signal (Hc) using at least some of a plurality of state signals (Q0, Q1, Q2) and a plurality of inverted state signals (X0, X1, X2).

[0040] The control unit (400) is intended to control a plurality of switches of the inverter (INV). To this end, it may be implemented by a gate driver and an EPLD (Erasable Programmable Logic Device). The control unit (400) detects sector numbers (1 to 6) where the rotor is located in a plurality of sectors (SECTOR 1 to 6) in which the complex space (CS) is divided by six boundary voltage vectors (V1 to V6) from a combination signal (Ha, Hb, Hc), which is a combination of a first rotor position signal (Ha), a second rotor position signal (Hb), and a third rotor position signal (Hc). Additionally, the control unit (400) can calculate the angle of the rotor based on the combination signal (Ha, Hb, Hc) and the sector numbers (1 to 6). And the control unit (400) can derive the time (T1) for applying the first boundary voltage vector of the corresponding sector and the time (T2) for applying the second boundary voltage vector from the sector number and the angle of the rotor. And the control unit (400) generates a control signal for controlling the switches of the inverter (INV) according to Space Vector Modulation (SVM or Space Vector PWM, SVPWM) based on the time (T1) for applying the first boundary voltage vector and the time (T2) for applying the second boundary voltage vector, and controls a plurality of switches of the inverter (INV) according to the generated control signal.

[0041] Next, a method for driving a motor based on a virtual sensor signal according to an embodiment of the present invention will be described. FIG. 4 is a flowchart illustrating a method for driving a motor based on a virtual sensor signal according to an embodiment of the present invention. FIG. 5 is a timing diagram illustrating a method for deriving a first rotor position signal according to an embodiment of the present invention. FIG. 6 and FIG. 7 are timing diagrams illustrating a method for deriving a second rotor position signal and a third rotor position signal according to an embodiment of the present invention. FIG. 8 is a conceptual diagram illustrating a method for deriving a sector number in a complex space according to an embodiment of the present invention. FIG. 9 and FIG. 10 are conceptual diagrams illustrating a control method based on space vector modulation according to an embodiment of the present invention.

[0042] Referring to FIG. 4, the voltage detection unit (100) detects the terminal voltage (Va) of one of the three phases of the motor (MT) for the voltage input from the inverter (INV) in step S110 by converting it into a divided voltage magnitude through resistors (R1, R2) connected in parallel to the input terminal.

[0043] The position derivation unit (200) derives a first rotor position signal (Ha) that simulates the signal of one of three Hall sensors virtually mounted on the motor (MT) based on the terminal voltage (Va) in step S120. That is, the three Hall sensors are not actually mounted on the motor (MT), but are assumed to be mounted on the motor (MT). In other words, the first rotor position signal (Ha) simulates the signal detected by one of the Hall sensors when it is assumed that three Hall sensors are mounted on the motor (MT). The method for deriving the first rotor position signal (Ha) in step S120 is explained in more detail as follows.

[0044] Referring to FIG. 5, first, the active filter (210) of the position extraction unit (200) derives a first lagging voltage (Va') having a sinusoidal wave lagged by 90 degrees through filtering of the divided terminal voltage (Va). Then, the integrator and zero-point detection circuit (220) lagged the first lagging voltage (Va') by 90 degrees (Va'') and detected the zero point (Vzc) to derive a first rotor position signal (Ha).

[0045] Next, the position estimation unit (300) derives a second rotor position signal (Hb) and a third rotor position signal (Hc) that simulate the signals of the remaining two Hall sensors among the three Hall sensors based on the first rotor position signal (Ha) in step S130. Similar to the first rotor position signal (Ha), the second rotor position signal (Hb) and the third rotor position signal (Hc) simulate the signals detected by the remaining two Hall sensors that are not the Hall sensor corresponding to the first rotor position signal (Ha), assuming that three Hall sensors are mounted on the motor (MT).

[0046] The method for deriving the second rotor position signal (Hb) and the third rotor position signal (Hc) of step S130 is explained in more detail as follows.

[0047] Referring to FIG. 6, the PLL circuit (310) first performs a 6x multiplication on the first rotor position signal (Ha) to generate a 6x multiplication signal (6X).

[0048] Then, the binary counter (320) rectifies the 6x multiplied signal (6X) to generate a rectified signal (RTF).

[0049] Next, referring to FIG. 7, the first Johnson counter (331) rectifies the signal ( A plurality of state signals (Q0, Q1, Q2) that are shifted in cycle units of the rectified signal are derived from ), and the second Johnson counter (332) is the inverted signal of the rectified signal ( A plurality of inverted state signals (X0, X1, X2) are derived from the rectified signal in cycle units.

[0050] Then, the logic circuit (340) derives the second rotor position signal (Hb) and the third rotor position signal (Hc) using at least some of the plurality of state signals (Q0, Q1, Q2) and the plurality of inverted state signals (X0, X1, X2).

[0051] According to one embodiment, the logic circuit (340) can derive a second rotor position signal (Hb) and a third rotor position signal (Hc) through a logic operation such as the following mathematical formula 1.

[0052]

[0053] Here, Hb represents the second rotor position signal, and Hc represents the third rotor position signal.

[0054] Additionally, Q0 and Q1 represent state signals calculated by the first Johnson counter (331). And X0 and X2 represent inverted state signals calculated by the second Johnson counter (332).

[0055] Next, in step S140, the control unit (400) detects the sector number (1 to 6) where the rotor is located in a plurality of sectors (SECTOR 1 to 6) in which the complex space (CS) is divided by six boundary voltage vectors (V1 to V6) from a combination signal (Ha, Hb, Hc) which is a combination of the first rotor position signal (Ha), the second rotor position signal (Hb), and the third rotor position signal (Hc).

[0056] As shown in FIG. 8, a complex space (CS) divided by boundary voltage vectors (V1 to V6) is illustrated. In this way, sector numbers can be derived based on the boundary voltage vectors (V1 to V6) where the Hall sensor signal changes.

[0057] Next, the control unit (400) calculates the angle of the rotor based on the combination signal (Ha, Hb, Hc) and sector number (1 to 6) in step S150. At this time, the control unit (400) can determine whether the sector number increases or decreases through the change in the combination signal (Ha, Hb, Hc), and can calculate the angle of the rotor by applying the following mathematical formula 2 according to the increase or decrease of the sector number.

[0058]

[0059] Here, θ represents the rotor angle. And STRN represents the sector number in complex space.

[0060] For example, if the combination signal changes to 101 or 100, it can be determined that it is increasing, and if the combination signal changes to 110 or 100, it can be determined that it is decreasing.

[0061] Next, the control unit (400) derives the time (T1) for applying the first boundary voltage vector and the time (T2) for applying the second boundary voltage vector of the corresponding sector from the sector number and the angle of the rotor in step S160. At this time, the control unit (400) can derive the time for applying the first boundary voltage vector and the time for applying the second boundary voltage vector according to the following mathematical formula 3.

[0062]

[0063]

[0064] Here, T1 represents the time for applying the first boundary voltage vector, T2 represents the time for applying the second boundary voltage vector, and Ts represents the sampling time. Also, V* represents the command voltage, and θ represents the rotor angle. And Vdc represents the DC power supply voltage.

[0065] Next, the control unit (400) generates a control signal to control the switch of the inverter (INV) according to Space Vector Modulation (SVM or Space Vector PWM, SVPWM) based on the time (T1) for applying the first boundary voltage vector and the time (T2) for applying the second boundary voltage vector in step S170.

[0066] Then, the control unit (400) controls a plurality of switches of the inverter (INV) according to the control signal in step S180.

[0067] According to the present invention, the rotor position can be derived solely from the terminal voltage component of a single phase, based on a method previously proposed for indirect rotor position detection, which involves connecting three phase terminal voltages in a Y-connection using resistors R having the same value and utilizing the voltage between neutral points inside the motor. In other words, the present invention converts the terminal voltage of a single phase into a divided magnitude through resistors connected in parallel and uses the resulting signal to detect rotor position information. The terminal voltage information detected in this way passes through an active filter and is compared with a zero-point detection circuit (ZCP) via an integration circuit to generate a virtual sensor signal that simulates a single-phase Hall sensor signal. In particular, the present invention derives the rotor angle using the sensor signal simulating the Hall sensor signal, generates a control signal for spatial vector modulation based on this, and controls the inverter switch to control the motor. Accordingly, stable sensorless operation over a wide speed range is possible at a lower cost than conventional sensorless methods.

[0068] Although the present invention has been described above using several preferred embodiments, these embodiments are illustrative and not limiting. As such, those skilled in the art will understand that various changes and modifications can be made in accordance with the doctrine of equivalents without departing from the spirit of the invention and the scope of rights set forth in the appended claims. Explanation of the symbols

[0069] 10: Driving device 100: Detector 200: Location extraction unit 210: Active Filter 220: Integration and Zero Detector 300: Position Estimation Unit 310: PLL circuit 320: Binary counter 331: The 1st Johnson Counter 332: The 2nd Johnson Counter 340: Logic circuit 400: Control unit

Claims

Claim 1 A method for driving an electric motor comprises: a voltage detection unit detecting a terminal voltage for one of the three phases of the electric motor with respect to a voltage input from an inverter, by converting the terminal voltage to a voltage-divided magnitude through a resistor connected in parallel to the input terminal; a position derivation unit deriving a first rotor position signal simulating a signal of one of three Hall sensors virtually mounted on the electric motor based on the terminal voltage; and a position estimation unit deriving a second rotor position signal and a third rotor position signal simulating the signals of the remaining two Hall sensors based on the first rotor position signal; wherein a control unit detecting a sector number where the rotor is located in a plurality of sectors divided by six boundary voltage vectors in a complex space from a combination signal which is a combination of the first rotor position signal, the second rotor position signal, and the third rotor position signal; and a control unit calculating the angle of the rotor based on the combination signal and the sector number. A method for driving an electric motor, further comprising: a step in which the control unit derives a time for applying a first boundary voltage vector and a time for applying a second boundary voltage vector of the corresponding sector from the sector number and the angle of the rotor; a step in which the control unit generates a control signal for controlling a switch of the inverter based on the time for applying the first boundary voltage vector and the time for applying the second boundary voltage vector; and a step in which the control unit controls a plurality of switches of the inverter according to the control signal. Claim 2 A method for driving an electric motor according to claim 1, wherein the step of deriving the first rotor position signal comprises: a step of deriving a first ground voltage having a sinusoidal wave that is 90 degrees grounded through filtering of the divided terminal voltage by an active filter; and a step of deriving the first rotor position signal by an integrator and a zero-point detection circuit grounding the first ground voltage by 90 degrees and detecting a zero point. Claim 3 A method for driving an electric motor according to claim 1, wherein the step of deriving the second rotor position signal and the third rotor position signal comprises: a step in which a PLL circuit performs a 6x multiplication on the first rotor position signal to generate a 6x multiplication signal; a step in which a binary counter rectifies the 6x multiplication signal to generate a rectified signal; a step in which a first Johnson counter derives a plurality of state signals shifted in units of the period of the rectified signal from the rectified signal; a step in which a second Johnson counter derives a plurality of inverted state signals in units of the period of the rectified signal from the inverted signal of the rectified signal; and a step in which a logic circuit derives the second rotor position signal and the third rotor position signal using at least some of the plurality of state signals and the plurality of inverted state signals. Claim 4 delete Claim 5 In claim 1, the step of calculating the angle of the rotor is performed by a control unit using a mathematical formula A method for driving an electric motor characterized by calculating the angle of the rotor according to the above, wherein θ is the angle of the rotor and STRN is a sector number in complex space. Claim 6 In paragraph 1, the step of generating the control signal is that the control unit [forms a mathematical formula] A method for driving a motor characterized by deriving a time for applying a first boundary voltage vector and a time for applying a second boundary voltage vector of the corresponding sector from the sector number and the angle of the rotor according to the above, wherein T1 is the time for applying the first boundary voltage vector and T2 is the time for applying the second boundary voltage vector, Ts is the sampling time, V* is the command voltage, θ is the electrical angle of the rotor, and Vdc is the DC power supply voltage. Claim 7 A device for driving an electric motor comprises: a voltage detection unit that detects a terminal voltage for one of the three phases of an electric motor with respect to a voltage input from an inverter by converting it into a voltage-divided magnitude through a resistor connected in parallel to the input terminal; a position derivation unit that derives a first rotor position signal simulating a Hall sensor signal of one of three Hall sensors virtually mounted on the electric motor based on the terminal voltage; and a position estimation unit that derives a second rotor position signal and a third rotor position signal simulating the remaining two Hall sensor signals of the three Hall sensors based on the first rotor position signal. A device for driving an electric motor, comprising: a combination signal which is a combination of the first rotor position signal, the second rotor position signal, and the third rotor position signal; a control unit which detects a sector number where the rotor is located in a plurality of sectors divided by six boundary voltage vectors in a complex space from the combination signal which is a combination of the first rotor position signal, the second rotor position signal, and the third rotor position signal; calculates the angle of the rotor based on the combination signal and the sector number; derives the time for applying the first boundary voltage vector and the time for applying the second boundary voltage vector of the corresponding sector from the sector number and the angle of the rotor; generates a control signal for controlling the switches of the inverter based on the time for applying the first boundary voltage vector and the time for applying the second boundary voltage vector; and further comprises a control unit which controls the plurality of switches of the inverter according to the control signal. Claim 8 delete

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