JPH1141983A - Motor controller and changing method of motor control - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor controller with a minimum loss in a stationary state, in which the difference between positive and negative sides of an output voltage from a power amplifier is corrected, and a changing method with a small loss in motor control, even when there is a difference in load constants, a carrier frequency is high, or a power element has poor characteristics. SOLUTION: A motor controller includes a PWM control amplifier 12 for detecting a deviation between a current command and a feed back current Ifb , a comparator 13 for comparing a carrier signal and the PWM control amplifier 12 and generating a pulse width modulation signal, and an analog switch 5 for receiving an input ±Vref and carrying out switching operation on the basis of the output signal of the comparator 13. In the PWM control, a rectangular wave signal, rectified in amplitude from the analog switch 5, is fed as a command signal to a power amplifier 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor control device having a power amplifier for controlling a current and controlling a motor, and a method of switching control by the motor control device, and more particularly to at least pulse width modulation (PWM). Pulse Width Mo
motor control device for controlling the motor by dulation) control, and linear amplification control and PWM in the motor control device.
The present invention relates to a motor control switching method for switching between control and motor control.

[0002]

2. Description of the Related Art An electric motor is generally controlled by changing or modulating a drive current of the electric motor in accordance with a command. In this case, as a current control method, generally, a method using pulse width modulation control (hereinafter, referred to as PWM control) and a method using linear amplification control are known. The PWM control is a method in which a power element such as a power bipolar transistor or a power MOS transistor is used in an on / off switching mode, and a current is adjusted by changing an on / off operation duty. This is a method of adjusting the current used in the linear operation region.

However, each of these control methods has some disadvantages. The PWM control has low loss and high efficiency. However, when the output current is small, the ratio of the pulsating component of the current increases, and the dead time (dead time, delay time, etc.) at the time of switching of the power element causes High-precision current control is difficult. On the other hand, linear amplification control has high control performance with good current resolution and linearity, but has a large power loss and is inefficient.

[0004] Therefore, by combining these two control methods to effectively combine the respective characteristics, specifically, by switching between the linear amplification control and the PWM control, control is performed with high efficiency and high accuracy. High-resolution current control becomes possible.

[0005] In the control of the motor, linear amplification control and P
As a switching method for switching between the WM control, a threshold value is set in advance to distinguish between a large current region (high efficiency region) and a small current region (high resolution region), and a command value (current command or thrust / torque command) is set. Etc.) and this threshold value, there is a method of switching between linear amplification control and PWM control in accordance with the result of comparison.

FIG. 6 is a block diagram showing the configuration of a conventional motor control device which switches between linear amplification control and PWM control by setting a threshold value as described above. Here, it is assumed that a three-phase motor 86 is used as the motor. Current command IU _ref , IV _ref , IW _ref for each phase for motor 86
Microprocessor 81 for generating as a digital value
And the current command IU _ref , I from the microprocessor 81
A D / A converter unit 82 that digitally / analog-converts V _ref and IW _ref into current commands IU, IV, and IW, respectively;
A power amplifier 83 that drives the motor 86 by supplying currents U, V, W corresponding to these three-phase current commands IU, IV, IW to the motor 86. Note that a current corresponding to the current command is supplied to the motor 86 so that the motor 86
Is called normal operation or servo-on.

[0007] Power amplifier unit 83, for each phase, the linear amplifier control amplifier 91 for detecting and amplifying a difference between a current command and a current feedback value I _fb, likewise current command and the current feedback value I _fb And a comparator 93 that generates a pulse-width modulated signal by comparing a carrier signal of a predetermined frequency with the output of the PWM control amplifier 92.
And one end of a resistor 96 is connected to the output terminal.
, An analog switch 84 that switches and outputs the output from the operational amplifier 95 and the output of the linear amplification control amplifier 91 that are input via the resistor 96, and an analog switch 84.
And a power amplifier 94 for inputting the output of
A power element is built in the power amplifier 94, and the output of the power amplifier 94 is used as a drive current of a corresponding phase.
It is supplied to the electric motor 86.

Between the connection point of the resistor 96 and the analog switch 84 and the ground point, two Zener diodes 97 are connected in series and have opposite polarities to limit the amplitude of the input voltage to the analog switch 84. Connected so that
Has been inserted. That is, the amplitude of the output voltage of the operational amplifier 95 is limited by the resistor 96 and the zener diode 97 to the sum of the zener voltage of the zener diode 97 and the forward voltage. At the time of the PWM control, the output signal subjected to the amplitude control becomes a command of the power amplifier 94, and the power is converted by the power amplifier 94. As a result, the electric motor 96 is driven with a current corresponding to the current command.

The analog switch 84 is configured to be switched by an instruction from the microprocessor 81. The microprocessor 81 has preset thresholds for distinguishing between a large current region (high efficiency region) and a small current region (high resolution region), and the microprocessor 81 has a command value (current command or thrust / torque command). ) Is compared with the threshold value, and the switching signal for the analog switch 84 is changed according to the result. As a result, the motor control device switches the analog switch 84 to the comparator 95 side at the time of a large current, and performs a PWM control to prevent a decrease in efficiency.
4 is switched to the linear amplification control amplifier 91 side, and linear amplification control is performed to perform highly accurate control.

Now, the loss P during linear amplification control
_d-LIN is represented by equation (1).

[0011]

(Equation 1) V _s is the supply _{voltage, R M, L M, V} M , respectively, the resistance value of the load (motor 86), the inductance value is a counter electromotive force, I _L is the output current, in V _o is the output voltage is there. In the case of a motor, the back electromotive voltage V _M is represented by an induced voltage constant of K _E and a speed of ω.
Then

[0012]

V _M = K _E × ω (2) If the velocity ω is known, the back electromotive force V _M can be obtained. Loss P _d-LIN during linear amplification control, load constants _{(R M, L M, V} M) depends heavily on. Also,
The loss _Pd-PWM at the time of the PWM control is represented by Expression (3).

[0013]

P _{d -PWM} = E _(sat) + E _sw (3) where E _(sat) is a saturation loss (stationary loss) and E _sw
Is the switching loss. It is known that the steady loss E _(sat) is proportional to the output current, and the switching loss E _sw is proportional to the switching frequency (frequency of the carrier signal).

FIG. 7 is a graph showing the relationship between the output current at a certain load and the loss, obtained from the equations (1) and (3).
In the case of the conventional motor control device described above, considering the loss P _d-PWM (point b in the figure) of the PWM control at the time of the rated current in the motor, the loss P _d-LIN during the linear amplification control is the same as this. An output current (point a in the figure) is obtained, and a command value (current command or the like) for generating the output current is set as a switching threshold. The switching threshold distinguishes a large current region (high-efficiency region) by PWM control and a small current region (high-resolution region) by linear amplification control.

However, when the load constant is different, the carrier frequency is high, or the characteristics of the power element are bad, the loss P ′ _d-PWM of the PWM control at the rated current (b ′ in the figure)
Point) may be larger than the loss P _d-LIN of the linear amplification control. This corresponds to a case where there are a plurality of points (points e in the figure) where the loss in the linear amplification control and the loss in the PWM control are the same within the range of the rated current. In such a case, even if the output current is in the large current region, the linear amplifier control can reduce the loss generated in the power amplifier. As a result, the above-described conventional motor control device and the above-described motor control switching method do not sufficiently reduce the loss, and accordingly increase the size of the radiator for the power element. As a result, it becomes difficult to reduce the size and cost of the motor control device.

FIG. 8 is a diagram showing an example of an output waveform from the power amplifier 94 of the motor control device shown in FIG. When a voltage gain of the power amplifier 94 and G, the PWM control of the normal operation voltage instruction to be input to the power amplifier 94 is the voltage gain G times, the output voltage V _o, an output current I _{o 'in} accordance with the current command, Output from the power amplifier 94. At this time, the steady loss E _(sat) in the power amplifier 94
Is represented by a hatched portion in the figure. In the case of the motor control device shown in FIG. 6, considering the case of PWM control, since the voltage command input to the power amplifier 94 is amplitude-controlled by the Zener diode, the amplitude limit value is determined by the diode. The limit value cannot be set freely, and the limit value of the amplitude is not very accurate. Furthermore, because a Zener diode is used,
There are problems such as the inability to operate at high speed. Further, unless this offset voltage is adjusted by the offset voltage of the operational amplifier 93, the amplitude of the positive side and the negative side of the voltage command will differ. That is, as shown in FIG. 8, the amplitude on the + V _s side and the amplitude on the −V _s side differ from each other with reference to the ground potential (GND), that is, 0V. When the difference in amplitude is generated in the positive and negative directions, the steady loss of the power amplifier 94 increases, causing the power amplifier to be damaged beyond the safe operating area (SOA) of the power amplifier or to operate within the safe operating area. As a result, there arises a problem that a heat radiation system of the power amplifier becomes large.

[0017]

As described above, in the conventional motor control device, the amplitude limit value is not very accurate during PWM control, high-speed operation is difficult, and the amplitude of the output voltage is positive and negative. There is a problem that the steady loss in the power amplifier section is large differently from the power side, and further, when switching between the PWM control and the linear amplification control, if the load constant is different or the carrier frequency is high, the characteristics of the power element are poor. In some cases, it is difficult to reduce loss, reduce size, and reduce cost.

An object of the present invention is to provide a motor control device in which the difference between the positive and negative amplitudes in the output voltage of a power amplifier is corrected to minimize the steady-state loss, and a difference in load constant and a high carrier frequency. In this case, it is an object of the present invention to provide a motor control switching method that can reduce the size of the device and reduce the cost even when the characteristics of the power element are poor.

[0019]

According to the present invention, there is provided a motor control apparatus comprising: a first amplifier for detecting a deviation between a current command and a current feedback; and comparing the first amplifier with a carrier signal to perform pulse width modulation. And a power amplifier that adjusts an output current in accordance with the signal output by the comparator, wherein the motor control device controls the motor with an output current from the power amplifier. A first analog switch that performs an input switching operation based on a signal to be input, and an output of the first analog switch is supplied as a command to the power amplifier.

[0020] In the motor control apparatus of the present invention, the gain of the power amplifier and G, the reciprocal 1 / G of the gain G as preset voltage V _{re f} with respect to the maximum output voltage of the power amplifier, a first analog switch Preferably has two inputs to which + V _ref and -V _ref are supplied as voltages, respectively, so that the first analog switch is driven by the output signal from the comparator. It is preferable that by performing the switching operation, the first analog switch outputs a pulse-width-modulated rectangular wave signal whose amplitude has been adjusted. A second amplifier for detecting a deviation between the current command and the current feedback; and a second analog switch for switching the output of the second amplifier and the output of the first analog switch and inputting the output to the power amplifier. Prepared, second
By switching the analog switch of
It is preferable to be driven by either WM (pulse width modulation) control or linear amplification control.

According to the motor control switching method of the present invention, the motor is driven by a power amplifier, and the motor is controlled by switching to one of linear amplification control and PWM (pulse width modulation) control. In the switching method, the loss value in the power amplifier section is obtained, the loss value is compared with a preset switching threshold value, and when the loss value exceeds the switching threshold value, the PWM control is performed. When the loss value is equal to or less than the switching threshold, the motor current is controlled by the linear amplification control.

In the motor control switching method according to the present invention, when the switching threshold value is set in advance, a current command is given to the power amplifier section while being changed at certain steps within the entire current control range for driving the motor. By doing
For each step, the loss of the power amplifier unit in the case of the linear amplification control and the loss of the power amplifier unit in the case of the PWM control are calculated, and the loss in the case of the linear amplification control and the case of the PWM control within a preset range. It is preferable that when the loss matches the loss, the matched loss is used as the switching threshold. The microprocessor compares the loss in the case of the linear amplification control with the loss in the case of the PWM control, and calculates the loss value of the power amplifier section by the microprocessor during the normal operation of the electric motor to switch the threshold value. Preferably, the microprocessor generates a switching signal for switching between the linear amplification control and the PWM control according to the comparison result.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION

<< First Embodiment >> FIG. 1 is a block diagram showing a configuration of a motor control device according to a first embodiment of the present invention. Also in this motor control device, a threshold value is set, and switching between linear amplification control and PWM control is performed.
Here, it is assumed that a three-phase motor 6 is used as the motor. The motor control device sets the threshold value and sets the current command IU _ref , IV _ref , I
A microprocessor 1 for generating W _ref as a digital value, and current commands IU _ref , I
V _ref, IW _ref digital / analog converter respectively current command IU, IV, and D / A converter unit 2, IW, these three-phase current command IU, IV, current corresponding to the IW U,
The power amplifier unit 3 supplies V and W to the electric motor 6 to drive the electric motor 6. A state in which a current corresponding to the current command is supplied to the motor 6 to drive the motor 6 is referred to as a normal operation or a servo-on state.

[0024] a power amplifier part 3, for each phase, the linear amplifier control amplifier 11 for detecting and amplifying a difference between a current command and a current feedback value I _fb, likewise current command and the current feedback value I _fb And a comparator 13 that generates a pulse width modulated signal by comparing a carrier signal of a predetermined frequency with the output of the PWM control amplifier 12.
An analog switch 5 that operates in response to a pulse-width signal output from the comparator 13, an analog switch 4 that switches and outputs the output from the analog switch 5 and the output of the linear amplification control amplifier 1, and the analog switch And a power amplifier 14 to which the output of C.4 is input. The power amplifier 14 performs linear amplification control and PW
A power element is provided as a common element for both the M control and the output from the power amplifier 14 is
The driving current of the corresponding phase is supplied to the electric motor 6. The analog switch 4 corresponds to the second analog switch, and switches between linear amplification control and PWM control. The analog switch 5 corresponds to the first analog switch, and has a rectangular wave signal during PWM control. Is used for amplitude correction. The linear amplification control amplifier 11 corresponds to the second amplifier, and the PWM control amplifier 12
Corresponds to the first amplifier.

The analog switch 5 has two inputs.
And the preset voltage is V_refAs these two
+ V for each input_refAnd -V_refIs supplied.
Voltage V _refIs the gain of the power amplifier 14 as G
The inverse of the gain G with respect to the maximum output voltage of the power amplifier 14
It is set as a voltage multiplied by the number 1 / G. like this
Operates the analog switch 5 by the output signal of the comparator 13.
The output signal of the analog switch 5
Is a constant voltage ± V_refWidth Modulated with Pulse Amplitude
Of the square wave signal. On the other hand, the analog switch 4
In response to an instruction (switch signal) from the microprocessor 1,
It is configured to switch. As mentioned above,
Microprocessor 1 has a large current region (high efficiency region) and a small current region.
The threshold for distinguishing between the current region (high-resolution region)
The microprocessor 1 sets the command value (power
Flow command or thrust / torque command) and this threshold.
And turn off the analog switch 4 according to the result.
Change the replacement signal.

At the time of a small current, the analog switch 4 switches to the side of the linear amplification control amplifier 11 to execute the linear amplification control. In the linear amplification control of the normal operation, a deviation between the current command and the current feedback value _Ifb is detected by the linear amplification control amplifier 11, and this deviation becomes a command to the power amplifier 14, and the power is converted by the power amplifier 14. . As a result, the electric motor 6 is driven by the current according to the current command. At the time of a large current, the analog switch 4 switches to the analog switch 5 side, and the PWM control is executed. At the time of the PWM control of the normal operation, a deviation between the current command and the current feedback value _Ifb is detected by the PWM control amplifier 12, and the comparator 13 compares the deviation with the carrier signal and outputs a pulse width modulated signal. This signal causes the analog switch 5 to operate. Thereby, as described above, a constant voltage, that is, ±
The pulse width modulated rectangular wave signal adjusted with the amplitude of _Vref is output from the analog switch 5, and the amplitude adjusted rectangular wave signal is commanded to the power amplifier 14, and the power is converted by the power amplifier 14. You. As a result, the electric motor 6 is driven by the current according to the current command.

FIG. 2 shows an output waveform of the power amplifier 14 of the motor control device during the PWM control.
At the time of the PWM control in the normal operation, the above-described voltage command having the amplitude of ± V _ref is multiplied by the voltage gain G by the power amplifier 14, and the power amplifier 14 _obtains V _(sat) = (± V _ref ×
The G) to output the output current I _o in accordance with the output voltage V _o and the current command obtained by the amplitude. At this time, the steady loss E _(sat) of the power amplifier 14 is simply

[0028]

[Number 4] E _(sat) = - it can be calculated as _{(V s V (sat))} × I o (4). This steady loss E _(sat) corresponds to the area of the hatched portion in FIG.

After all, in the present embodiment, the power amplifier unit 3
The analog switch 5 is provided in the PWM control system, and a preset voltage (± V _ref ) which is the reciprocal 1 / G of the gain G of the power amplifier with respect to the maximum output voltage of the power amplifier 14
Is input to the analog switch 5. The analog switch 5 outputs a pulse width modulated rectangular wave signal whose amplitude has been adjusted by the input value, and the power amplifier 14 is driven by the rectangular wave signal. Therefore, the steady loss of the power amplifier 14 is minimized. It becomes possible to suppress. Further, the amplitude can be set freely and accurately by changing the input value to the analog switch 5, that is, ± V _ref .
Since a rectangular wave signal is generated by switching with the analog switch 5, high-speed operation is possible.

<< Second Embodiment >> Next, a second embodiment of the present invention will be described. This embodiment relates to a method of switching motor control. In the case where the load constant is different, the carrier frequency is high, or the characteristics of the power element in the power amplifier are poor, the linear amplification control for the same output current is performed. By detecting a point at which the loss and the loss in the PWM control are equal to each other and setting a loss value (current value) at that point as a switching threshold, and switching between the linear amplification control and the PWM control by the switching threshold, The loss is further reduced. FIG. 3 is a block diagram illustrating an example of a configuration of a motor control device used for performing the switching method according to the second embodiment. This motor control device is different from the motor control device of the first embodiment shown in FIG. 1 in that an analog switch for adjusting the amplitude is not provided, and the output of the comparator 13 is directly input to the analog switch 4. Differs in that Of course, in this embodiment, the use of the motor control device of the above-described first embodiment is sufficiently possible. In this embodiment, it is assumed that the microprocessor 1 can calculate the power loss in the power amplifier unit 3.

The procedure of the motor control switching method according to the present embodiment will be described below with reference to the flowchart of FIG. This procedure is for obtaining a switching threshold value for switching between the linear amplification control and the PWM control. The procedure for obtaining the switching threshold value is executed prior to the normal operation of the motor control.

First, as processing 1, the analog switch 4
Is switched to the linear amplification control amplifier 11 side, and the control method is fixed to the linear amplification control, and the current command is changed step by step with a certain step width over the entire current control range of the motor load. A current is caused to flow through the motor 6, and the loss P _{dL IN} of the linear amplification control is calculated by the above equation (1).
Is calculated. In this case, the microprocessor 1 changes the current command in a step-like manner and outputs it to the power amplifier unit 3, fixes the analog switch 4 on the linear amplification control side, calculates the loss P _d-LIN , and calculates The result is stored in the storage area of the microprocessor 1. At this time, a current flows through the electric motor 6, so that the electric motor 6 needs to be locked. The step width is, for example, 1/10 of the rated current.

Next, as processing 2, the analog switch 4
Is switched to the comparator 13 side, and the control method is fixed to the PWM control. The current command is changed step by step by a certain step width over the entire current control range of the motor load. Apply the current and the above equation
According to (2), the loss _Pd-PWM of the PWM control is calculated. In this case, the microprocessor 1 changes the current command in a step-like manner and outputs it to the power amplifier unit 3, fixes the analog switch 4 on the PWM control side, calculates the loss _Pd-PWM, and calculates the calculation result. Is stored in the storage area of the microprocessor 1. Also at this time, since electric current flows through the electric motor 6, the electric motor 6 needs to be locked. The step width is, for example, 1/10 of the rated current. Then, as processing 3, the microprocessor 1 determines the loss value P stored in the storage area by the processing 1 and processing 2 described above.
_d-LIN and _{Pd -PWM} are compared for each current command step, and the process proceeds to processing 4.

In process 4, when both loss values match within a preset range, the loss value is set as a switching threshold (points c and d in FIG. 5), and the process ends. When the current command is continuously changed, as shown in FIG.
Even if there is a point (point e in the figure) where the loss in the M control and the loss in the linear amplification control match, if the current command is changed in a step-like manner, the preset range may vary depending on the step width. If it is too small, both loss values may not match within that range. Therefore, as a preset range, in the case where the loss in the linear amplification control is smaller than the loss in the PWM control in the large current region,
The matching loss value must always be determined.

If there is no loss value that matches even when the range is set as described above, that is, in a large current region, P
Under the condition that the loss of the linear amplification control is always larger than the loss of the WM control, the same value as described in the prior art, that is, the PWM control loss value at the rated current is set to the switching threshold value I do. When the switching threshold value is set as described above, the normal operation of the motor control is executed.
The microprocessor 1 constantly calculates the loss value in the power amplifier unit 3, compares the switching threshold value with the calculated loss value, and outputs a switching signal to the analog switch 4 according to the comparison result. This switches between the linear amplification control and the PWM control.

FIG. 5 shows the switching threshold values (points c and d) obtained by this embodiment under the condition that the loss in the linear amplification control is smaller than the loss in the PWM control in the large current region. Point) and the switching threshold value (point b) of the conventional method, and the relationship between the output current and the loss in these cases is shown as a graph. According to the present embodiment, the loss which is the determined switching threshold is smaller than the switching threshold of the conventional method by the amount obtained by subtracting the loss at the point c or d from the loss at the point b. Become. If the switching threshold value is reduced, the loss generated in the power amplifier can be reduced, and the radiator for the power element can be reduced.

[0037]

As described above, the motor control apparatus of the present invention minimizes the steady loss in the power amplifier by adjusting the amplitude of the rectangular wave signal for PWM control using the analog switch. And the amplitude can be set freely and accurately,
In addition, there is an effect that high-speed operation becomes possible. The switching method of the motor control according to the present invention calculates the loss in the linear amplification control and the loss in the PWM control, compares the calculation results, and sets the same point of the loss as the switching threshold value in the PWM.
By switching between control and linear amplification control,
There is an effect that the power amplifier section can achieve low loss, small size, and low cost.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a motor control device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an output waveform from a power amplifier of the motor control device shown in FIG.

FIG. 3 is a block diagram illustrating an example of a configuration of a motor control device to which a motor control switching method according to a second embodiment of the present invention is applied.

FIG. 4 is a flowchart illustrating a method for switching motor control according to a second embodiment.

FIG. 5 is a graph illustrating a relationship between an output current and a loss during PWM control and linear amplification control according to the second embodiment.

FIG. 6 is a block diagram illustrating a configuration of a conventional motor control device.

FIG. 7 is a graph showing a relationship between an output current and a loss during PWM control and linear amplification control in the motor control device shown in FIG. 6;

8 is a diagram showing an output waveform from a power amplifier of the motor control device shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Microprocessor 2 D / A converter part 3 Power amplifier part 4,5 Analog switch 6 Motor 11 Linear amplification control amplifier 12 PWM control amplifier 13 Comparator 14 Power amplifier

Claims (6)

[Claims] A first amplifier for detecting a deviation between a current command and a current feedback; a comparator for comparing the first amplifier with a carrier signal to output a pulse-width-modulated signal; A power amplifier for adjusting an output current in accordance with a signal to be output, wherein the motor control device controls an electric motor with an output current from the power amplifier. 1. An electric motor control device, comprising: an analog switch, wherein an output of the first analog switch is supplied as a command to the power amplifier. 2. A method according to claim 1, wherein the gain of the power amplifier is G, and a reciprocal 1 / G of the gain G with respect to a maximum output voltage of the power amplifier is a predetermined voltage _Vref. And + V _ref and −V _ref are supplied as voltages to the input, respectively,
2. The motor control device according to claim 1, wherein the analog switch performs a switching operation based on an output signal from the comparator to output a pulse width modulated rectangular wave signal whose amplitude has been adjusted from the first analog switch. 3. 3. A second amplifier for detecting a difference between the current command and the current feedback, and a second amplifier for switching an output of the second amplifier and an output of the first analog switch and inputting the output to the power amplifier. 3. The electric motor according to claim 1, further comprising: a second analog switch, wherein the electric motor is driven by one of PWM (pulse width modulation) control and linear amplification control by switching the second analog switch. 4. Control device. 4. A method for switching motor control in which a motor is driven by a power amplifier and the motor is switched to one of a linear amplification control and a PWM (pulse width modulation) control to control the motor. Calculating a loss value in the section, comparing the loss value with a preset switching threshold value, and when the loss value exceeds the switching threshold value, controlling the motor current in the PWM control; When the loss value is equal to or less than the switching threshold value, the motor current is controlled by the linear amplification control. 5. The power amplifier in the case of the linear amplification control for each of the steps by giving a current command to the power amplifier while changing the current for every certain step within the entire current control range of the motor drive. When the loss in the linear amplification control and the loss in the PWM control match within a preset range, the loss of the power amplifier unit is calculated in the case of the PWM control. The coincident loss is set as the switching threshold,
The method for switching motor control according to claim 4. 6. A comparison between a loss in the case of the linear amplification control and a loss in the case of the PWM control is performed by a microprocessor, and during a normal operation of the electric motor, the loss value of the power amplifier unit is reduced by the microprocessor. 6. The motor control according to claim 5, wherein the microprocessor generates a switching signal for switching between the linear amplification control and the PWM control according to the comparison result. Switching method.