Control device for motor

Abstract

To provide a control device capable of continuously driving a motor without limiting an input to the motor.SOLUTION: A control device 101 of a motor 103 driven by an inverter (a power converter 102) includes a gate signal generation unit 114, a determination unit (a motor component loss / temperature determination unit 116) and a voltage waveform adjustment unit 117. The gate signal generation unit 114 compares a three-phase voltage signal with a carrier wave to generate a gate signal to be input to the inverter. The determination unit compares component temperature of the motor 103 with management temperature (a threshold value) of a component. When the component temperature of the motor 103 exceeds the management temperature of the component, the voltage waveform adjustment unit 117 changes the carrier wave to increase the magnet temperature of the motor 103.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a control device for an electric motor. [Background technology]

[0002] With growing global awareness of protecting the global environment, the automotive industry is also shifting from conventional internal combustion engines to electrification using motors that do not emit greenhouse gases during operation. Electric drive systems, which are essential for the electrification of automobiles, are equipped with power converters and electric motors to extract driving force from the electricity supplied by the battery, as well as control devices to operate these as intended. Even in electrified automobiles, vehicle driving performance such as acceleration / deceleration, top speed, and continuous driving characteristics remains the same as that of internal combustion engine-driven vehicles. Unlike internal combustion engines, electric motors installed in electric drive systems do not directly burn, so there is no need to manage combustion temperature.

[0003] However, in the process of converting electrical energy through electromagnetic circuits and outputting rotational power, losses occur in each component. These losses cause components to heat up, which can lead to irreversible performance degradation depending on the component. Losses continue to occur, especially during continuous driving, when components continue to generate heat, so performance is restricted to prevent the component temperature from rising.

[0004] To thermally protect components, the temperature is monitored at the coil end, where it is easy to attach a temperature sensor, and the relationship between the temperature sensor value and the temperature of each component is obtained through analysis, etc., so that the temperature does not exceed the control temperature set for each component.When the temperature sensor value reaches a threshold set so that the temperature of each component does not exceed the control temperature, the input to the motor is limited to stop the increase in loss during operation, thereby suppressing heat generation from the components.

[0005] Patent Document 1 shows a method for preventing thermal demagnetization due to an increase in magnet temperature by calculating magnet loss, which is a factor in an increase in magnet temperature, from a formula using harmonic components from input information when the motor is driven, and changing a control signal to reduce this loss when it exceeds a certain value.

[0006] Furthermore, Patent Document 2 discloses a method of estimating the magnet temperature using the harmonic components of the input, similar to Patent Document 1. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2022-018168 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-122857 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the methods shown in Patent Documents 1 and 2, the input is limited to thermally protect the components, but there are cases where the temperature of the components exceeds the control temperature at the desired operating point and continuous operation is not possible.

[0009] An object of the present invention is to provide a control device that can continuously drive an electric motor without limiting the input to the electric motor. [Means for solving the problem]

[0010] In order to achieve the above object, the present invention provides a control device for an electric motor driven by an inverter, comprising: a gate signal generation unit that compares a three-phase voltage signal with a carrier wave to generate a gate signal to be input to the inverter; a determination unit that compares a component temperature of the electric motor with a control temperature of the component; and a voltage waveform adjustment unit that changes the carrier wave and increases the magnet temperature of the electric motor when the component temperature of the electric motor exceeds the control temperature of the component. [Effects of the Invention]

[0011] According to the present invention, it is possible to continuously drive an electric motor without limiting the input power to the electric motor. Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 illustrates a first embodiment. [Figure 2] FIG. 4 is a diagram showing the relationship between the input current and the residual magnetic flux density of the magnet of the electric motor according to the first embodiment. [Figure 3] FIG. 4 is a diagram showing the relationship between the magnet temperature and the residual magnetic flux density of the magnet of the electric motor according to the first embodiment. [Figure 4] 2 shows an example of a rotor cross section of the electric motor according to the first embodiment, and magnetic poles and axes of a magnetic circuit cross section. [Figure 5] FIG. 4 is a diagram showing the relationship between the magnet temperature of the electric motor according to the first embodiment and the input current and the d-axis current for field weakening. [Figure 6] FIG. 4 is a diagram showing the relationship between the magnet temperature and the winding temperature of the electric motor according to the first embodiment. [Figure 7] FIG. 4 is a diagram showing the relationship between the magnet temperature and the winding temperature of an electric motor that is not the subject of the first embodiment. [Figure 8] FIG. 10 is a diagram illustrating a second embodiment. [Figure 9] FIG. 10 is a diagram illustrating a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Embodiment 1] A first embodiment of the present invention will be described. The object of this embodiment is to provide a control device that can continuously drive an electric motor by, for example, equalizing the heat between components by manipulating the harmonic components of the input rather than limiting the input to the electric motor.

[0014] Figure 1 shows the basic configuration of the drive system. The drive system is composed of a control device 101 that generates an input command (gate signal) for generating a drive force at a desired operating point, a power converter 102 (inverter) that converts the power from the vehicle's power source to be supplied to an electric motor 103 based on the input command generated by the control device 101, and the electric motor 103 that receives the power supply from the power converter 102 and generates a drive force for the vehicle.

[0015] The control device 101 is, for example, a microcomputer, and is composed of a processor such as a CPU (Central Processing Unit), a storage device such as a memory, an input / output circuit, a gate driver, etc. Sensor values ​​are input to the control device 101 via the input / output circuit from various sensors, such as a current sensor that measures the current of the electric motor 103 and an angle sensor that measures the rotation angle of the rotor of the electric motor 103.

[0016] Although not shown in Figure 1, the output of the electric motor 103 is transmitted to the axle via a reduction gear in vehicles where the electric motor 103 is the main driving source, such as electric vehicles and plug-in hybrid vehicles. In hybrid vehicles, the output is transmitted to the axle via a transmission or a power split mechanism. There are no particular limitations on the type of the power converter 102. There are no particular limitations on the type of the electric motor 103, other than the use of magnets.

[0017] Control device 101 includes current command generation unit 111 that generates a current command value for generating a driving force at a desired operating point, current control unit 112 that converts the current command value output from current command generation unit 111 into a voltage signal, three-phase conversion unit 113 that converts the voltage signal into a three-phase voltage signal, and gate signal generation unit 114 that generates a gate signal to be input to power converter 102 based on the three-phase voltage signal output from three-phase conversion unit 113. Control device 101 also includes current waveform component calculation unit 115 that calculates components included in the current waveform when power is supplied to electric motor 103, electric motor component loss / temperature determination unit 116 that calculates loss and component temperature generated in components of electric motor 103 from the current waveform components output by the current waveform component calculation unit, and voltage waveform adjustment unit 117, which will be described later.

[0018] When it is determined that the component temperature of the electric motor 103 exceeds a management temperature set in advance for each component, the electric motor component loss / temperature determination unit 116 outputs an adjustment command signal for correcting the gate signal output by the gate signal generation unit 114. The voltage waveform adjustment unit 117 converts the output adjustment command signal into an adjusted voltage waveform (carrier wave), which is a voltage waveform for correcting the gate signal. The adjusted voltage waveform (carrier wave) is input to the gate signal generation unit 114.

[0019] Here, the method of calculating the current waveform components in current waveform component calculation section 115 is not particularly specified, and a map of dq-axis inductances for each operating point may be prepared to calculate the dq-axis current at a desired operating point.

[0020] Furthermore, the method for calculating component losses of the electric motor 103 in the electric motor component loss / temperature determination unit 116 is not particularly specified. One example of a method for calculating component losses is to prepare a loss map in which component losses are calculated by electromagnetic field analysis for each operating point, and to perform two-dimensional interpolation of component losses at a desired operating point. Other examples of calculation methods include an approximation formula based on the results of electromagnetic field analysis of the electric motor 103, or an empirical formula based on measurement results of an actual machine. Calculation formulas include, for example, formulas consisting of rotational frequency and current harmonic components, their orders, and coefficients.

[0021] Next, the method of calculating the component temperatures of the electric motor 103 in the electric motor component loss / temperature determination unit 116 is not particularly specified. For example, the component temperatures may be calculated using a thermal calculation tool based on a thermal circuit network. Alternatively, the component temperatures may be calculated using a thermal fluid analysis tool.

[0022] The motor component loss / temperature determination unit 116 determines that the temperature of each component of the motor 103 calculated so far does not exceed the management temperature set for each component. The management temperature of the component varies for each component. For some components like the conducting wire forming the coil, the heat resistance grade may be defined, and for some components like the magnet, it may be defined as the temperature at which irreversible thermal demagnetization does not occur. For example, materials that are prone to performance degradation under high heat, such as recycled magnets, may be used.

[0023] When the winding exceeds the management temperature, the motor component loss / temperature determination unit 116 changes the voltage waveform when the management temperature is exceeded and calculates the conditions for reducing the current flowing through the component.

[0024] FIG. 2 shows the current flowing through the winding when outputting torque while suppressing the magnet flux in the weak field weakening region. In a motor using magnets, an induced electromotive force is generated as the rotational speed increases. To cancel this induced electromotive force, a current for suppressing the magnet flux is input to the winding to output torque even in the high rotation region. This is called weak field weakening control, and the current for suppressing the magnet flux is called the weak field weakening current. The weak field weakening current is input as the component of the d-axis shown in FIG. 4.

[0025] FIG. 4 shows a schematic diagram of the rotor. The center of the magnetic pole where the inductance increases is called the d-axis, and the axis advanced by 90 electrical degrees from the d-axis is called the q-axis. Here, there are other methods for reducing the magnet flux. In this embodiment, for example, the method of reducing the magnet flux by increasing the magnet temperature is utilized.

[0026] FIG. 3 shows the relationship between temperature and magnet flux. FIG. 3 shows the characteristics of a magnet where when the temperature of the magnet is A < A', the magnetic flux density of A' is lower than that of A. Since there are some magnets whose magnet flux decreases when the temperature is low depending on the type of magnet, the type of magnet is not particularly limited.

[0027] As an example, we will explain the case where an electric motor employing a magnet with the characteristics shown in Figure 3 is used. As shown in Figure 3, the magnetic flux of the magnet can be reduced by increasing the magnet temperature, and therefore by reducing the field-weakening current that was the cause of the increase in winding temperature, the resistance loss of the winding can be reduced, preventing the increase in winding temperature.

[0028] One possible method for increasing the magnet temperature is to increase magnet loss. Although there are no particular limitations on the method for increasing magnet temperature, one method is to increase the sum of harmonic components contained in the d-axis component of the field-weakening current, which can increase magnet loss.

[0029] As the magnet loss increases, the magnet temperature rises, resulting in a decrease in the magnet magnetic flux. To increase the harmonic components of the d-axis current, one method is to correct the gate signal in order to change the signal input from the power converter 102 to the electric motor 103. Because the gate signal is based on the three-phase voltage waveform, the signal input to the electric motor 103 can be changed by changing the shape of the three-phase voltage waveform.

[0030] For example, voltage waveform adjustment unit 117 changes the shape of the carrier wave and shifts the phase of the pulses of the three-phase voltage waveform. When electric motor 103 is driven by the three-phase voltage waveform with the phase-shifted pulses, current waveform component calculation unit 115 calculates the current components. From the calculated current components, electric motor component loss / temperature determination unit 116 calculates the winding temperature and determines whether the winding temperature is below the control temperature, i.e., whether thermal protection is required.

[0031] Depending on the operating conditions, the process from changing the carrier wave shape to determining the temperature is repeated to calculate the carrier wave shape that will bring the magnet and winding into thermal equilibrium. At this time, increasing the magnet temperature will decrease the winding temperature, as shown in Fig. 6. However, this method does not cover operating conditions where the magnet temperature exceeds the control temperature when the winding temperature falls below the control temperature, as shown in Fig. 7.

[0032] The main features of the first embodiment can be summarized as follows:

[0033] As shown in Fig. 1, a control device 101 for an electric motor 103 driven by an inverter (power converter 102) includes a gate signal generation unit 114, a determination unit (electric motor component loss / temperature determination unit 116), and a voltage waveform adjustment unit 117. The gate signal generation unit 114 compares a three-phase voltage signal with a carrier wave to generate a gate signal to be input to the inverter. The determination unit (electric motor component loss / temperature determination unit 116) compares the component temperature of the electric motor 103 with a component management temperature (threshold value). If the component temperature of the electric motor 103 exceeds the component management temperature, the voltage waveform adjustment unit 117 changes the carrier wave and increases the magnet temperature of the electric motor 103.

[0034] Increasing the magnet temperature of the electric motor 103 reduces the magnetic flux of the magnet and reduces the field-weakening current. As a result, the resistance loss of the winding is reduced, and the winding temperature can be lowered. This allows the electric motor 103 to be continuously driven without limiting the input to the electric motor 103. In this embodiment, the voltage waveform adjuster 117 changes the carrier wave when it receives an adjustment command signal from the electric motor component loss / temperature determiner 116.

[0035] The voltage waveform adjusting unit 117 changes the frequency of the carrier wave, or changes the slope and period of the triangular wave that is the carrier wave, thereby adjusting the magnet temperature of the electric motor 103.

[0036] In detail, the voltage waveform adjusting unit 117 changes the carrier wave to increase the sum of the d-axis current harmonic components contained in the field weakening current, which increases magnet loss and can raise the magnet temperature.

[0037] The determination unit (motor component loss / temperature determination unit 116) compares the magnet temperature of the motor 103 with the magnet's management temperature. The voltage waveform adjustment unit 117 changes the carrier wave within a range in which the magnet temperature of the motor 103 is lower than the magnet's management temperature (FIG. 6). This makes it possible to suppress thermal demagnetization of the magnet.

[0038] The determination unit (motor component loss / temperature determination unit 116) compares the winding temperature of the motor 103 with the winding management temperature. The voltage waveform adjustment unit 117 changes the carrier wave within a range in which the winding temperature of the motor 103 is lower than the winding management temperature (FIG. 6). This makes it possible to thermally protect the winding.

[0039] The judgment unit (motor component loss / temperature judgment unit 116) increases the torque of the motor at the operating point so that the difference ΔT1 between the magnet temperature of the motor 103 and the management temperature of the magnet becomes equal to the difference ΔT2 between the winding temperature of the motor 103 and the management temperature of the winding (FIG. 6).

[0040] When the carrier wave is changed to increase the magnet temperature of the electric motor 103, the phase current also decreases as shown in Fig. 5, and the torque of the electric motor 103 decreases. Therefore, by increasing the torque so that the difference ΔT1 and the difference ΔT2 are equal, it is possible to suppress torque fluctuations.

[0041] In this embodiment, the determination unit (motor component loss / temperature determination unit 116) inputs a correction torque (torque increment) to the current waveform component calculation unit 115 until the difference ΔT1 from the magnet's management temperature becomes equal to the difference ΔT2 between the winding temperature of the motor 103 and the management temperature of the winding (FIG. 1). Here, the current waveform component calculation unit 115 derives a current order component corresponding to the sum of the command torque and the correction torque using a map or the like, and inputs the current order component to the motor component loss / temperature determination unit 116. The determination unit (motor component loss / temperature determination unit 116) updates the magnet temperature using the current order component. When the input of the correction torque (torque increment) is no longer received, the current waveform component calculation unit 115 inputs a correction signal to the current command generation unit 111, which is a command to add the cumulative value of the correction torque to the command torque. The current command generation unit 111 derives a current command value corresponding to the sum of the command torque and the cumulative value of the correction torque using a map or the like.

[0042] In this embodiment, the determination unit (motor component loss / temperature determination unit 116) calculates the winding temperature of the motor 103 using current harmonic components (current order components) input from the inverter (power converter 102) to the motor 103. Since a sensor for detecting the winding temperature is not required, manufacturing costs can be reduced.

[0043] [Embodiment 2] A second embodiment of the present invention will now be described. Fig. 8 shows the basic configuration of this embodiment. The difference from the first embodiment is that component temperatures are input from a temperature detector 818 attached to the electric motor 103. In this embodiment, by directly acquiring the component temperatures of the electric motor 103, the accuracy of the component temperatures input to the electric motor component loss / temperature determination unit 116 can be improved.

[0044] The main features of the second embodiment can be summarized as follows.

[0045] 8, the determination unit (electric motor component loss / temperature determination unit 116) acquires the component temperature of electric motor 103 from a temperature detector 818 provided in electric motor 103. The component temperature is detected with high accuracy by temperature detector 818, which improves the accuracy of thermally protecting the components.

[0046] [Embodiment 3] A third embodiment of the present invention will now be described. Figure 9 shows the basic configuration of this embodiment. The difference from the first and second embodiments is that the adjusted shape of the voltage waveform is read from an adjusted voltage waveform map 919, which is a database, for each possible pattern of the operating conditions and the carrier wave waveform. In this embodiment, the time required to change the carrier wave waveform can be shortened, and the calculation volume is reduced.

[0047] The main features of the third embodiment can be summarized as follows.

[0048] The control device 101 includes a map (adjusted voltage waveform map 919) that stores a carrier wave associated with a current harmonic component input from the inverter (power converter 102) to the electric motor 103, such that the magnet temperature of the electric motor 103 is lower than the magnet's management temperature, the winding temperature of the electric motor 103 is lower than the winding's management temperature, and the difference between the electric motor's magnet temperature and the magnet's management temperature is equal to the difference between the electric motor's winding temperature and the winding's management temperature. The control device 101 also includes a current waveform component calculation unit 115 that calculates the current harmonic component. The voltage waveform adjustment unit 117 derives, from the map, a carrier wave associated with the current harmonic component (current order component) calculated by the current waveform component calculation unit 115. The voltage waveform adjustment unit 117 changes the carrier wave used in the gate signal generation unit 114 to the carrier wave derived from the map. This reduces calculation costs.

[0049] The present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0050] Furthermore, the above-described configurations, functions, etc. may be realized in part or in whole by hardware, for example, by designing them as integrated circuits. Furthermore, the above-described configurations, functions, etc. may be realized in software by a processor interpreting and executing a program that realizes each function. Information such as the programs, tables, and files that realize each function can be stored in a memory, a recording device such as a hard disk or SSD (Solid State Drive), or a recording medium such as an IC card, SD card, or DVD.

[0051] The embodiment of the present invention may have the following aspects.

[0052] (1) A control device for an electric motor driven by a power conversion device, comprising: a current waveform component calculation unit that calculates current harmonic components at a predetermined operating point; a component temperature determination unit that calculates the magnet temperature of the electric motor using the current harmonic components and generates an adjustment command signal for a voltage waveform; and a voltage waveform adjustment unit that generates an adjusted voltage waveform based on the adjustment command signal, wherein the component temperature determination unit calculates the magnet temperature of the electric motor and generates the adjustment command signal to increase the magnet temperature, and the voltage waveform adjustment unit generates the adjusted voltage waveform based on the adjustment command signal.

[0053] (2) The component temperature determination unit compares the calculated magnet temperature with a preset magnet control temperature, determines whether the magnet temperature has room to rise above the control temperature, and adjusts the voltage waveform by modifying the carrier wave of the adjustment command signal. A control device for an electric motor according to (1).

[0054] (3) The motor control device described in (2) calculates the winding temperature of the motor using the adjusted current harmonic components, compares it with a preset winding control temperature, and modifies the carrier wave to obtain the temperature.

[0055] (4) A control device for an electric motor as described in (3), wherein the component temperature determination unit increases the output or torque of the operating point so that the thermal margins of the magnet and the winding are equal when the winding temperature has a thermal margin relative to the winding management temperature.

[0056] (5) The motor control device according to (4), wherein the control device that generates the input signal changes a carrier frequency of the input command.

[0057] (6) The motor control device according to (5), wherein the control device that generates the input signal changes the slope and period of the carrier waveform of the input command.

[0058] (7) The motor control device according to (6), wherein the component temperature determination unit determines the component temperature of the motor based on the result of a temperature detection device installed in the motor.

[0059] (8) The motor control device according to (7), wherein the voltage waveform adjustment unit generates the adjusted voltage waveform by reading a database in which the adjustment command signal is patterned.

[0060] According to (1)-(8), at an operating point where one of the motor's components reaches the control temperature and continuous operation becomes difficult, the temperature of the component in question can be kept within the control temperature without limiting the input, allowing continuous operation. At this time, components other than the component in question may rise in temperature because they are no longer within the minimum loss range, but the input command is corrected so that both components are within the control temperature range.

[0061] Furthermore, in an electric drive system having a power converter that converts power from a vehicle power source and an electric motor that generates driving force for the vehicle, a control device that generates an input command signal to the power converter according to the operating conditions of the vehicle has a motor loss / temperature calculation unit that calculates the loss and temperature generated in the electric motor from the input command signal, and when the loss / temperature determination unit determines that the magnet temperature of the electric motor in the field-weakening region has a margin above the management temperature, the magnet loss may be increased in order to raise the temperature of the magnet, reduce the magnet magnetic flux, and suppress the field-weakening current.

[0062] Since magnet loss increases as the sum of the harmonic components of the field-weakening current increases, the harmonic components of the current are increased by changing the carrier waveform, thereby suppressing the temperature rise of the windings and thermally protecting the motor components. [Explanation of symbols]

[0063] 101...Control device 102...Power converter 103...Electric motor 111...Current command generation section 112...Current control section 113...Three-phase conversion unit 114...Gate signal generating unit 115...Current waveform component calculation section 116...Motor component loss / temperature determination unit 117...Voltage waveform adjustment unit 818...Temperature detector 919...Adjusted voltage waveform map

Claims

1. A control device for an electric motor driven by an inverter, a gate signal generating unit that compares the three-phase voltage signals with a carrier wave to generate gate signals to be input to the inverter; a determination unit that compares the component temperature of the electric motor with a control temperature of the component; a voltage waveform adjusting unit that changes the carrier wave and increases a magnet temperature of the motor when the component temperature of the motor exceeds a management temperature of the component; A control device for an electric motor comprising:

2. The motor control device according to claim 1, The determination unit The magnet temperature of the motor is compared with the magnet control temperature, The voltage waveform adjustment unit The carrier wave is changed within a range in which the magnet temperature of the electric motor is lower than the management temperature of the magnet. A control device for an electric motor.

3. The motor control device according to claim 2, The determination unit Comparing the winding temperature of the motor with the winding control temperature, The voltage waveform adjustment unit The carrier wave is changed within a range in which the winding temperature of the motor is lower than the management temperature of the winding. A control device for an electric motor.

4. The motor control device according to claim 3, The determination unit The torque of the motor at an operating point is increased so that the difference between the magnet temperature of the motor and the management temperature of the magnet becomes equal to the difference between the winding temperature of the motor and the management temperature of the winding. A control device for an electric motor.

5. The motor control device according to claim 4, The voltage waveform adjustment unit Change the frequency of the carrier wave A control device for an electric motor.

6. The motor control device according to claim 4, The voltage waveform adjustment unit Change the slope and period of the triangular wave, which is the carrier wave A control device for an electric motor.

7. The motor control device according to claim 1, The determination unit The temperature of the components of the electric motor is acquired from a temperature detector provided in the electric motor. A control device for an electric motor.

8. The motor control device according to claim 4, a map that stores carrier waves that correspond to current harmonic components input from the inverter to the motor, where the magnet temperature of the motor is lower than the management temperature of the magnet, the winding temperature of the motor is lower than the management temperature of the winding, and the difference between the magnet temperature of the motor and the management temperature of the magnet is equal to the difference between the winding temperature of the motor and the management temperature of the winding; a current waveform component calculation unit that calculates the current harmonic components, The voltage waveform adjustment unit deriving, from the map, a carrier wave associated with the current harmonic component calculated by the current waveform component calculation unit; The carrier wave used in the gate signal generating unit is changed to a carrier wave derived from the map. A control device for an electric motor.

9. The motor control device according to claim 2, The determination unit The winding temperature of the electric motor is calculated using the current harmonic components input from the inverter to the electric motor. A control device for an electric motor.

10. The motor control device according to claim 1, The voltage waveform adjustment unit By changing the carrier wave, the sum of the d-axis current harmonic components contained in the field weakening current is increased. A control device for an electric motor.

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