electric motor

Abstract

To suppress increase in loss.SOLUTION: An electric motor includes a control unit. The control unit includes a current coordinate conversion unit, a speed control unit, and a phase adjustment unit. The current coordinate conversion unit converts an actual current flowing in each phase of a motor into a d-axis current and a q-axis current. The speed control unit calculates a d-axis current command value and a q-axis current command value by PI control using a difference between an angular velocity and an angular velocity command value. When a modulation factor is less than a predetermined threshold, the phase adjustment unit adjusts the d-axis current command value and the q-axis current command value by gradually subtracting a current phase, which is a phase difference between a composite vector of the d-axis current command value and the q-axis current command value and a q-axis, by a predetermined phase adjustment amount.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to electric motors. [Background technology]

[0002] When driving a motor using sensorless control of an inverter, it is necessary to estimate the rotational position of the motor's rotor. Sensorless control is a control method that drives a motor without using a hardware position sensor by estimating the rotational position of the rotor using software. The rotational position of the rotor can be estimated based on the induced voltage generated in the coils of the motor.

[0003] When the rotor rotates at a low speed, the induced voltage becomes small, and the accuracy of estimating the rotational position of the rotor decreases. Furthermore, even if the rotation speed is constant, if the input voltage is large and the modulation rate is small, the accuracy of estimating the rotation position will decrease due to the influence of dead time. In this case, although the influence of voltage error due to dead time is reduced by dead time compensation, it is difficult to completely eliminate the voltage error. The voltage error due to dead time does not depend on the modulation rate.

[0004] On the other hand, the higher the input voltage and the smaller the modulation factor, the smaller the inverter output voltage, and therefore the smaller the modulation factor, the larger the proportion of voltage error relative to the output voltage.As a result, when the input voltage is high and the modulation factor is small, the influence of the voltage error relative to the output voltage reduces the accuracy of estimating the rotational position.

[0005] The motor control device disclosed in Patent Document 1 sets the d-axis current command value to a value greater than 0 when the motor rotation speed is lower than a predetermined rotation speed. This increases the induced voltage generated in the coil. As the induced voltage increases, the accuracy of estimating the rotation position improves. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2018-196309 Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Document 1, when the motor rotation speed is lower than a predetermined rotation speed, if the input voltage fluctuates and increases, the modulation factor fluctuates and decreases, and the estimation accuracy of the rotation position decreases. Also, the d-axis current command value may become excessively large. In this case, the increase in the motor current may increase losses. [Means for solving the problem]

[0008] The electric motor that solves the above problem is an electric motor comprising: a motor having a rotor and a stator wound with three-phase coils; an inverter unit having switching elements and driving the motor; and a control unit that receives an angular velocity command value and controls the switching elements using a PWM signal, wherein the control unit generates the PWM signal based on a voltage command value and a carrier frequency, and includes a current coordinate conversion unit that converts actual currents flowing through each phase of the motor into d-axis current and q-axis current; a current coordinate conversion unit that calculates an induced voltage generated in the coil, estimates the rotational position of the rotor based on the induced voltage, and converts the actual currents flowing through each phase of the motor into d-axis current and q-axis current based on the rotational position. The present invention provides a speed control unit that calculates a d-axis current command value and a q-axis current command value by PI control using a difference between the angular velocity estimated by the angular velocity estimation unit and the angular velocity command value, a modulation factor calculation unit that calculates a modulation factor of the voltage command value, and a phase adjustment unit that, when the modulation factor calculated by the modulation factor calculation unit is less than a predetermined threshold, subtracts in a stepwise manner a current phase that is a phase difference between the q-axis and a composite vector of the d-axis current command value and the q-axis current command value by a predetermined phase adjustment amount, thereby adjusting the d-axis current command value and the q-axis current command value.

[0009] When the modulation rate is less than a predetermined threshold, the phase adjustment unit subtracts the current phase in stages by the phase adjustment amount. This increases the motor current. As the motor current increases, the output voltage of the inverter unit increases. Because the modulation rate increases, the estimation accuracy of the rotational position can be improved. By gradually subtracting the current phase by the phase adjustment amount until the modulation rate becomes equal to or greater than a predetermined threshold, the current phase is no longer subtracted by the phase adjustment amount once the modulation rate becomes equal to or greater than the predetermined threshold. Because the motor current is prevented from becoming excessively large, it is possible to prevent losses from increasing due to an increase in the motor current.

[0010] For the electric motor, the control unit may increase the phase adjustment amount until the phase adjustment amount becomes zero when the modulation factor is equal to or greater than the predetermined threshold value. For the electric motor, when the phase adjustment amount is smaller than a predetermined adjustment amount lower limit, the control unit may set the phase adjustment amount to the adjustment amount lower limit. [Effects of the Invention]

[0011] According to the present invention, it is possible to prevent the loss from increasing. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic configuration diagram of a motor control device. [Figure 2] FIG. 10 is a diagram for explaining a current phase. [Figure 3] FIG. 10 is a diagram showing the relationship between a current phase command value and torque of an IPM motor. [Figure 4] 10 is a flowchart illustrating a process performed by a phase adjustment unit. [Figure 5] FIG. 10 is a diagram illustrating a phase adjustment amount. [Figure 6] FIG. 10 is a diagram showing the relationship between a current phase command value and torque when a motor current is changed. [Figure 7] FIG. 10 is a diagram showing the relationship between a current phase command value and torque of an SPM motor. [Figure 8]FIG. 10 is a diagram showing current vectors when the current phase of the SPM motor is changed to the negative side. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of the electric motor will now be described. As shown in FIG. 1, the electric motor M1 includes a motor 11. The motor 11 has a rotor 12 and a stator 13 around which three-phase coils U, V, and W are wound. The motor 11 is a three-phase motor equipped with three coils U, V, and W. The motor 11 is an IPM (Interior Permanent Magnet) motor in which a permanent magnet is embedded inside the rotor 12. The motor 11 may be mounted in any device. For example, the motor 11 is a drive source for a compressor in a refrigeration circuit mounted in a vehicle, or a drive source for an air pump, a hydrogen pump, or the like mounted in a fuel cell vehicle.

[0014] The electric motor M1 includes a motor driving device 10. The motor driving device 10 includes a battery BA, a smoothing capacitor C, an inverter unit 21, a phase current detection unit 22, a voltage detection unit 23, and a control unit 30.

[0015] The inverter unit 21 includes six switching elements Q1 to Q6 and diodes D1 to D6. For example, IGBTs (insulated gate bipolar transistors) are used as the switching elements Q1 to Q6. When the switching elements Q1 to Q6 and the diodes D1 to D6 are integrated, MOSFETs (metal oxide semiconductor field effect transistors) are used. The switching elements Q1 and Q2 are connected in series to each other. The switching elements Q3 and Q4 are connected in series to each other. The switching elements Q5 and Q6 are connected in series to each other. The diodes D1 to D6 are connected in parallel to the switching elements Q1 to Q6, respectively. A battery BA is connected to each switching element Q1 to Q6 via a smoothing capacitor C.

[0016] The connection line between switching element Q1 and switching element Q2 branches off midway and is connected to coil U. The connection line between switching element Q3 and switching element Q4 branches off midway and is connected to coil V. The connection line between switching element Q5 and switching element Q6 branches off midway and is connected to coil W.

[0017] The phase current detection unit 22 detects phase currents for at least two phases. In this embodiment, the phase current detection unit 22 detects a u-phase current Iu, a v-phase current Iv, and a w-phase current Iw. The phase currents for two of the three phases may be detected, and the phase current for the remaining phase may be calculated from the phase currents for the two phases. The u-phase current Iu, the v-phase current Iv, and the w-phase current Iw are actual currents flowing through the respective phases of the motor 11.

[0018] The voltage detection unit 23 detects the input voltage Vi input from the battery BA to the inverter unit 21. When mounted on a vehicle, the voltage value of the input voltage Vi fluctuates, so the voltage detection unit 23 detects the fluctuating input voltage Vi.

[0019] <Control unit> The control unit 30 includes a processor and a storage unit. The processor may be, for example, a central processing unit (CPU), a graphics processing unit (GPU), or a digital signal processor (DSP). The storage unit includes a random access memory (RAM) and a read-only memory (ROM). The storage unit stores program code or instructions configured to cause the processor to execute a process. The storage unit, i.e., a computer-readable medium, includes any available medium accessible by a general-purpose or special-purpose computer. The control unit 30 may be configured with a hardware circuit such as an application-specific integrated circuit (ASIC) or a field-programmable gate array (FPGA). The control unit 30, which is a processing circuit, may include one or more processors operating according to a computer program, one or more hardware circuits such as an ASIC or an FPGA, or a combination thereof.

[0020] The control unit 30 controls the inverter unit 21 by sensorless control. Sensorless control is a method of controlling the inverter unit 21 without using a hardware position sensor that detects the rotational position of the rotor 12 of the motor 11. The motor 11 is driven by controlling the inverter unit 21.

[0021] The control unit 30 includes a current coordinate conversion unit 31, an angular velocity estimation unit 32, subtraction units 33 and 36, a speed control unit 34, a phase adjustment unit 35, a current control unit 37, a two-phase / three-phase conversion unit 38, and a modulation factor calculation unit 39.

[0022] The current coordinate converter 31 converts the phase currents Iu, Iv, and Iw into a d-axis current Id and a q-axis current Iq based on the rotational position θ of the rotor 12 estimated by the angular velocity estimator 32. For example, the current coordinate converter 31 converts the phase currents Iu, Iv, and Iw in a three-phase (U, V, W) fixed coordinate system into currents Iα and Iβ in a two-phase (α, β) fixed coordinate system. The current coordinate converter 31 converts the currents Iα and Iβ into a d-axis current Id and a q-axis current Iq in a two-phase (d, q) rotating coordinate system using the rotational position θ. The d-axis and q-axis are coordinate axes of the dq coordinate system. The dq coordinate system is a coordinate system that rotates together with the rotor 12 of the motor 11.

[0023] The angular velocity estimator 32 estimates the rotational position θ of the rotor 12 of the motor 11 based on the d-axis current Id and q-axis current Iq output from the current coordinate converter 31 and the d-axis voltage command value Vd* and q-axis voltage command value Vq* calculated by the current controller 37. For example, the angular velocity estimator 32 calculates induced voltages generated in the coils U, V, and W based on the d-axis current Id and q-axis current Iq, the d-axis voltage command value Vd* and the q-axis voltage command value Vq*, and constants determined by the motor 11. The angular velocity estimator 32 then estimates the rotational position θ based on the induced voltages. The angular velocity estimator 32 also estimates the angular velocity ω of the rotor 12 based on the rotational position θ.

[0024] Subtraction unit 33 calculates the difference Δω between angular velocity command value ω* and the angular velocity ω estimated by angular velocity estimation unit 32. Angular velocity command value ω* is input to control unit 30 from a higher-level control device of the vehicle.

[0025] The speed control unit 34 calculates a d-axis current command value Id* and a q-axis current command value Iq* based on the difference Δω. The speed control unit 34 calculates the d-axis current command value Id* and the q-axis current command value Iq* by using, for example, feedback control so that the difference Δω converges to 0. As the feedback control, for example, PI control can be used.

[0026] As shown in Figure 2, the current vector Ia that creates the rotating magnetic field can be expressed as a resultant vector of the d-axis current Id and the q-axis current Iq. The phase difference between the q-axis and the current vector Ia is defined as the current phase β.

[0027] As shown in Figure 3, there is a correlation between the current phase β and torque. The correlation between the current phase β and torque varies depending on the magnitude of the motor current. The d-axis current command value Id* and the q-axis current command value Iq* are calculated to obtain the current phase β at which the torque becomes maximum. The phase difference between the q-axis and current vector Ia*, which is a resultant vector of the d-axis current command value Id* and the q-axis current command value Iq*, is defined as the current phase command value β*.

[0028] As shown in FIG. 1, the phase adjustment unit 35 adjusts the current phase command value β* in accordance with the modulation factor M calculated by the modulation factor calculation unit 39. When the current phase command value β* is adjusted, the d-axis current command value Id* and the q-axis current command value Iq* change. The phase adjustment unit 35 calculates the adjusted d-axis current command value Id*' and the adjusted q-axis current command value Iq*' obtained by adjusting the current phase command value β*. The adjusted current phase command value β* is defined as the adjusted current phase command value β*'. The process of calculating the adjusted d-axis current command value Id*' and the adjusted q-axis current command value Iq*' will be described in detail below. The following process is repeatedly performed at a predetermined control period.

[0029] <Processing performed by the phase adjustment unit> As shown in FIG. 4, in step S1, the phase adjustment unit 35 determines whether the modulation factor M is less than a predetermined threshold. The predetermined threshold is a predetermined value. If the modulation factor M is less than the predetermined threshold, the estimation accuracy of the rotational position θ by the angular velocity estimation unit 32 decreases. The predetermined threshold for the modulation factor M is set to a value at which the estimation accuracy of the rotational position θ becomes unacceptable. If the determination result in step S1 is positive, the phase adjustment unit 35 performs the process of step S2. If the determination result in step S1 is negative, the phase adjustment unit 35 performs the process of step S10.

[0030] In step S2, the phase adjustment unit 35 adjusts the current phase command value β* to be smaller. That is, the current phase command value β* is subtracted by the phase adjustment amount α. As shown in FIG. 5, the phase adjustment amount α is an adjustment amount for the current phase command value β* determined by the speed control unit 34. The phase adjustment amount α is predetermined to be a smaller value each time the processing of step S2 is performed. For example, each time the processing of step S2 is performed, the current phase command value β* is subtracted by the phase adjustment amount α. That is, the current phase command value β* changes stepwise to the negative side. Note that FIG. 5 shows the relationship between the current phase command value β* and the phase adjustment amount α in a certain cycle.

[0031] Next, in step S3, the phase adjustment unit 35 determines whether the phase adjustment amount α is smaller than a predetermined adjustment amount lower limit. The phase adjustment amount α decreases each time the process of step S2 is performed, but the smaller the phase adjustment amount α, the smaller the torque. For this reason, an adjustment amount lower limit is set for the phase adjustment amount α to prevent the torque from becoming excessively small. The adjustment amount lower limit is set to a value that can prevent the torque from becoming excessively small. For example, the adjustment amount lower limit is set so that the current phase command value β* does not become less than −90 [deg]. If the determination result of step S3 is positive, the phase adjustment unit 35 performs the process of step S4. If the determination result of step S3 is negative, the phase adjustment unit 35 performs the process of step S5.

[0032] In step S4, the phase adjuster 35 sets the phase adjustment amount α to the adjustment amount lower limit. After completing the process of step S4, the phase adjuster 35 performs the process of step S5. In step S5, the phase adjustment unit 35 adjusts the d-axis current command value Id* and the q-axis current command value Iq* to obtain the adjusted d-axis current command value Id*' and the adjusted q-axis current command value Iq*'. The phase adjustment unit 35 calculates a current vector Ia*, which is a composite vector of the d-axis current command value Id* and the q-axis current command value Iq*, from the d-axis current command value Id* and the q-axis current command value Iq*. The phase adjustment unit 35 subtracts the phase adjustment amount α from the current phase command value β*. The value obtained by this subtraction is the adjusted current phase command value β*'. The phase adjustment unit 35 adjusts the d-axis current command value Id* and the q-axis current command value Iq* based on the adjusted current phase command value β*' to calculate the adjusted d-axis current command value Id*' and the adjusted q-axis current command value Iq*'. Specifically, the phase adjuster 35 calculates the adjusted d-axis current command value Id*' and the adjusted q-axis current command value Iq*' from the magnitude of the current vector Ia*' and the adjusted current phase command value β*'.

[0033] In step S10, the phase adjustment unit 35 adjusts the current phase command value β* so that it is larger. That is, the phase adjustment amount α is subtracted from the current phase command value β*. As shown in FIG. 5, the phase adjustment amount α is an adjustment amount for the current phase command value β* determined by the speed control unit 34. The phase adjustment amount α is predetermined to be larger each time the process of step S10 is performed. For example, each time the process of step S10 is performed, the current phase command value β* is subtracted by the phase adjustment amount α. That is, the current phase command value β* changes stepwise to the positive side. In this case, the phase adjustment amount α in step S10 may be the same value as or different from the phase adjustment amount α in step S2. When the phase adjustment amount α in step S10 and the phase adjustment amount α in step S2 are set to different values, the phase adjustment amount α in step S2 may be larger than the phase adjustment amount α in step S10.

[0034] Next, in step S11, the phase adjustment unit 35 determines whether the phase adjustment amount α is greater than 0. If the determination result in step S11 is negative, the phase adjustment unit 35 performs the process of step S5. If the determination result in step S11 is positive, the phase adjustment unit 35 performs the process of step S12.

[0035] In step S12, the phase adjustment unit 35 sets the phase adjustment amount α to 0. Even if the phase adjustment amount α becomes a value greater than 0 in step S10, the phase adjustment amount α is set to 0 in step S12. The maximum value of the phase adjustment amount α is 0. If the modulation factor M is equal to or greater than a predetermined threshold, the phase adjustment unit 35 increases the phase adjustment amount α until the phase adjustment amount α becomes 0. After completing the processing of step S12, the phase adjustment unit 35 performs the processing of step S5.

[0036] 1, the subtraction unit 36 ​​calculates the difference ΔId between the adjusted d-axis current command value Id*′ and the d-axis current Id. The subtraction unit 36 ​​calculates the difference ΔIq between the adjusted q-axis current command value Iq*′ and the q-axis current Iq.

[0037] The current control unit 37 calculates a d-axis voltage command value Vd* and a q-axis voltage command value Vq* based on the differences ΔId and ΔIq. The current control unit 37 calculates the d-axis voltage command value Vd* and the q-axis voltage command value Vq* by using, for example, feedback control so that the differences ΔId and ΔIq converge to 0. As the feedback control, for example, proportional-integral control can be used.

[0038] The two-phase / three-phase converter 38 converts the d-axis voltage command value Vd* and the q-axis voltage command value Vq* into a u-phase voltage command value Vu*, a v-phase voltage command value Vv*, and a w-phase voltage command value Vw* based on the rotational position θ of the rotor 12 estimated by the angular velocity estimator 32. For example, the two-phase / three-phase converter 38 converts the d-axis voltage command value Vd* and the q-axis voltage command value Vq* into voltage command values ​​Vα* and Vβ* in coordinates from the dq coordinate system to the αβ coordinate system. The two-phase / three-phase converter 38 converts the two-phase voltage command values ​​Vα* and Vβ* into three-phase voltage command values ​​Vu*, Vv*, and Vw*. The inverter unit 21 is controlled based on the voltage command values ​​Vu*, Vv*, and Vw*. More specifically, a PWM signal is generated based on the voltage command values ​​Vu*, Vv*, Vw* and the carrier frequency, and the switching elements Q1 to Q6 are controlled by the PWM signal.

[0039] The modulation factor calculation unit 39 calculates the modulation factor M of the voltage command value from the input voltage Vi of the inverter unit 21 and the voltage command value. The modulation factor M is a value obtained by dividing the voltage command value for the motor 11 by the input voltage Vi input to the inverter unit 21. The voltage command value is defined as the square root of the sum of the square of the d-axis voltage command value Vd* and the square of the q-axis voltage command value Vq*. The modulation factor calculation unit 39 calculates the modulation factor M from the following equation (1).

[0040]

number

[0041] When the modulation factor M is less than a predetermined threshold, the phase adjuster 35 subtracts the phase adjustment amount α from the current phase command value β*. The adjusted current phase command value β*' changes from the current phase command value β* to the negative side. As a result, the current phase β changes to the negative side. If the current phase β at the time when the phase adjuster 35 determines that the modulation factor M is less than the predetermined threshold is defined as the current phase P1, the current phase P1 changes to the negative side, resulting in the current phase P2. As can be seen from FIG. 6 , torque momentarily decreases when the current phase P1 changes to the negative side and becomes the current phase P2. The motor current increases by the amount corresponding to the torque decrease. More specifically, the speed controller 34 calculates the d-axis current command value Id* and the q-axis current command value Iq* so that the motor current increases to maintain the torque at the current phase P1. As shown in FIG. 6 , the motor current increases so that the difference between the torque at the current phase P1 and the torque at the current phase P2 decreases. In the example shown in FIG. 6 , the motor current changes from the motor current corresponding to line L11 to the motor current corresponding to line L12.

[0042] As the motor current increases, the output voltage of the inverter unit 21 increases. As the output voltage of the inverter unit 21 increases, the modulation factor M increases. More specifically, by shifting the current phase β to the negative side, the d-axis current Id changes to the positive side. When the d-axis current Id changes to the positive side, it can be seen from the following equation (2) that the voltage vector Va (=√(Vd*^2+Vq*^2)), which is the composite vector of the d-axis voltage Vd and the q-axis voltage Vq, increases. As a result, the output voltage increases, and the modulation factor M increases.

[0043]

number

[0044] If the modulation factor M does not become equal to or greater than the predetermined threshold value even when the current phase P1 is changed to the negative current phase P2, the phase adjustment unit 35 reduces the phase adjustment amount α. As a result, the current phase changes to a current phase P3 that is more negative than the current phase P2. The motor current further increases as the current phase P2 changes to the current phase P3. As shown in FIG. 6, the motor current increases so that the difference between the torque at the current phase P2 and the torque at the current phase P3 decreases. In the example shown in FIG. 6, the motor current corresponding to line L12 changes to the motor current corresponding to line L13. For convenience of illustration, the phase difference between the current phase P1 and the current phase P2 and the phase difference between the current phase P2 and the current phase P3 are shown as different in FIG. 6, but they may be the same.

[0045] Each time it is determined that the modulation factor M is less than the predetermined threshold, the phase adjustment amount α is reduced, thereby adjusting the d-axis current command value Id* and the q-axis current command value Iq* so that the current phase β changes stepwise to the negative side. If the phase adjustment amount α in step S2 is made larger than the phase adjustment amount α in step S10, the modulation factor M can be increased in a short time. By changing the current phase β stepwise to the negative side until the modulation factor M becomes equal to or greater than the predetermined threshold, the current phase β no longer changes to the negative side when the modulation factor M becomes equal to or greater than the predetermined threshold.

[0046] When it is determined that the modulation factor M is equal to or greater than a predetermined threshold, the phase adjuster 35 increases the phase adjustment amount α until the phase adjustment amount α becomes 0. As a result, when the modulation factor M becomes equal to or greater than the predetermined threshold, the motor current gradually decreases. If the phase adjustment amount α in step S2 is made larger than the phase adjustment amount α in step S10, the modulation factor M can be increased gradually. This can improve the stability of the control.

[0047] [Effects of this embodiment] (1) When the modulation factor M is less than a predetermined threshold, the phase adjustment unit 35 subtracts the phase adjustment amount α from the current phase command value β* to change the current phase command value β* to the negative side. Since an increase in the motor current increases the modulation factor M, the estimation accuracy of the rotational position θ can be improved. Furthermore, the phase adjustment unit 35 gradually changes the current phase β to the negative side until the modulation factor M becomes equal to or greater than a predetermined threshold. Once the modulation factor M becomes equal to or greater than the predetermined threshold, the current phase β no longer changes to the negative side. This prevents the motor current from becoming excessively large due to an excessive change in the current phase β to the negative side. This prevents an increase in loss due to an increase in the motor current.

[0048] (2) When the modulation factor M is equal to or greater than a predetermined threshold, the phase adjuster 35 increases the phase adjustment amount α, thereby shifting the current phase β to the negative side and reducing the motor current that has increased. This reduces the increase in loss.

[0049] (3) When the phase adjustment amount α is smaller than the adjustment amount lower limit, the phase adjuster 35 sets the phase adjustment amount α to the adjustment amount lower limit, thereby preventing the phase adjustment amount α from becoming a value smaller than the adjustment amount lower limit. [Example of change] The embodiment can be modified as follows: The embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0050] The control unit 30 may be used to control the motor 11, which is a surface permanent magnet (SPM) motor in which a permanent magnet is provided on the surface of the rotor 12. As shown in FIG. 7, in the case of an SPM motor, torque is maximized when the current phase command value β* is 0. The control unit 30 adjusts the current phase command value β* so that the current phase β changes to the negative side, as in the case of an IPM motor. Lines L21 and L22 in FIG. 7 show the correlation between the current phase command value β* and torque. Line L22 shows the correlation between the current phase command value β* and torque when the motor current is greater than that of line L21. When the modulation factor M is less than a predetermined threshold, the phase adjustment unit 35 adjusts the current phase command value β*. As a result, the current phase P11 changes to the negative side, resulting in a change to the current phase P12. As the current phase P11 changes to the current phase P12, the motor current corresponding to line L21 changes to the motor current corresponding to line L22. Although omitted in FIG. 7, the phase adjustment amount α is gradually reduced during the process in which the current phase P11 changes to the current phase P12. That is, FIG. 6 shows only the first current phase P11 and the last current phase P12 among the current phases that change stepwise to the negative side.

[0051] 8, the d-axis current Id changes to the positive side as the current phase β changes to the negative side, which increases the output voltage of the inverter unit 21 and therefore increases the modulation factor M.

[0052] When the modulation factor M is equal to or greater than a predetermined threshold, the phase adjuster 35 may set the phase adjustment amount α to 0 in one process, instead of gradually increasing the phase adjustment amount α until it becomes 0. [Explanation of symbols]

[0053] M1...electric motor, Q1 to Q6...switching elements, U, V, W...coils, 11...motor, 21...inverter unit, 30...control unit, 31...current coordinate conversion unit, 32...angular velocity estimation unit, 34...speed control unit, 35...phase adjustment unit, 39...modulation rate calculation unit.

Claims

1. a motor having a rotor and a stator wound with three-phase coils; an inverter unit having a switching element and driving the motor; a control unit that receives an angular velocity command value and controls the switching elements using a PWM signal; An electric motor comprising: The control unit generating the PWM signal based on a voltage command value and a carrier frequency; a current coordinate conversion unit that converts the actual current flowing through each phase of the motor into a d-axis current and a q-axis current; an angular velocity estimation unit that calculates an induced voltage generated in the coil, estimates a rotational position of the rotor based on the induced voltage, and estimates an angular velocity of the rotor based on the rotational position; a speed control unit that calculates a d-axis current command value and a q-axis current command value by PI control using a difference between the angular velocity estimated by the angular velocity estimator and the angular velocity command value; a modulation factor calculation unit that calculates a modulation factor of the voltage command value; and a phase adjustment unit that, when the modulation factor calculated by the modulation factor calculation unit is less than a predetermined threshold, subtracts in a stepwise manner a current phase, which is a phase difference between a q-axis and a composite vector of the d-axis current command value and the q-axis current command value, by a predetermined phase adjustment amount, thereby adjusting the d-axis current command value and the q-axis current command value.

2. The electric motor according to claim 1 , wherein the control unit increases the phase adjustment amount until the phase adjustment amount becomes zero when the modulation rate is equal to or greater than the predetermined threshold value.

3. 3. The electric motor according to claim 1, wherein the control unit sets the phase adjustment amount to the adjustment amount lower limit when the phase adjustment amount is smaller than a predetermined adjustment amount lower limit.

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