JP2002272197A - Electric motor control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To start an AC electric motor very stably, even if errors occur in the computation of an output frequency of an inverter. SOLUTION: In an electric motor control device, that is provided with an inverter circuit that converts DC power into AC power of desired voltage and frequency and that supplies the AC power of the inverter circuit to an AC electric moor to operate a variable speed drive, a lower limit means 15 is provided that gives the lower limit to a frequency, that is the output of a frequency calculating means 11 that calculates the frequency of a voltage to be impressed to the AC electric motor, based on a torque voltage reference, an excited voltage reference, a torque-constituent current, and an excited-constituent current, in such a way that it will not decrease to a given level or lower.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an AC motor such as an induction motor using an inverter to which a speed sensorless vector control is applied, and more particularly to a control device for an AC motor in which an error occurs in calculation of an inverter output frequency. The present invention relates to an electric motor control device that can be started in a very stable manner.

[0002]

2. Description of the Related Art Conventionally, when an AC motor such as an induction motor is driven, a frequency of a voltage applied to the induction motor is calculated from a torque voltage reference and an excitation voltage reference, and a slip frequency is subtracted from the frequency. The motor speed is estimated to drive the induction motor.

FIG. 15 is a block diagram showing a configuration example of a conventional motor control device of this kind.

In FIG. 15, 1 is a DC power supply, 2 is an inverter circuit for converting DC power of the DC power supply 1 into AC power,
Reference numeral 3 denotes an induction motor driven by the output of the inverter circuit 2.

[0005] In general, these main circuits are often configured as shown in the circuit diagram of FIG. 16, for example.

The U-phase current Iu and the W-phase current Iw flowing through the induction motor 3 are detected by a current detector 4.

The motor current coordinate converter 5 converts the U-phase current Iu and the W-phase current Iw into a torque component current (hereinafter referred to as “torque current”) Iq and an excitation component current (hereinafter “excitation”) based on the output voltage reference phase θ0. Current) is separated into each component of Id.

The current detected by the current detector 4 can be separated into a torque current and an exciting current even if a combination of any two phases other than the U-phase and the W-phase or a three-phase full current is used.

The speed controller 6 generates a torque reference T * such that the deviation between the speed reference ωr * and the estimated speed ωr becomes zero.

The vector controller 7 determines the torque reference T *
And a torque component current reference (hereinafter, referred to as “torque current reference”) based on the estimated speed ωr and the magnetic flux reference φ *.
Each component of Iq * and magnetic flux component current reference (hereinafter referred to as “excitation current reference”) Id * is separated and controlled.

The slip frequency calculator 8 calculates the slip frequency ωs based on the torque current reference Iq * and the magnetic flux reference φ *.

The current controller 9 controls the torque current reference Iq.
The torque voltage reference Vq * and the excitation voltage reference Vd * are generated such that the deviation between * and the torque current Iq and the deviation between the excitation current reference Id * and the excitation current Id become zero.

The voltage reference coordinate converter 10 converts the coordinates of the torque voltage reference Vq * and the excitation voltage reference Vd * based on the output voltage reference phase θ0, and applies the three-phase output voltage reference Vu *, Vv * and Vw * are output.

The frequency calculator 11 calculates a torque voltage reference Vq
Based on * and the excitation voltage reference Vd *, the frequency (hereinafter referred to as “inverter output frequency”) ω0 of the voltage applied to the induction motor 3 is output.

Although not explicitly shown in FIG. 15, the torque current Iq and the excitation current Id, or the torque current reference Iq * and the excitation current reference Id * may be used as inputs to the frequency calculator 11.

The estimated speed calculator 12 sets a value obtained by subtracting the slip frequency ωs from the inverter output frequency ω0 as the estimated speed ωr.

The integrator 13 integrates the inverter output frequency ω0 and outputs the output voltage reference phase θ0.

The PWM controller 14 controls the three-phase output voltage references Vu *, Vv *, Vw * and the inverter output frequency ω0
Based on the above, the driving signal G is output so that the three-phase output voltage of the inverter circuit 2 becomes the three-phase output voltage reference Vu *, Vv *, Vw *.

The inverter circuit 2 converts the DC power of the DC power supply 1 into AC power based on the drive signal G, and supplies the AC power to the induction motor 3 to perform variable speed driving.

Such control is generally called vector control, and it is known that control performance similar to that of a separately excited DC motor can be obtained.

In particular, a control as shown in FIG. 15 without using a speed sensor is called speed sensorless vector control.

In this type of vector control, stable field control can be performed by controlling the exciting current, and excellent speed response and speed control accuracy can be realized by controlling the torque current.

Each of the above controllers and arithmetic units is often constituted by an electronic circuit (not shown), a calculation by a microprocessor (not shown), or a combination thereof.

The operation of each of the above-mentioned controllers and arithmetic units is a well-known technique, and a detailed description thereof will be omitted here.

[0025]

However, the conventional motor control device as described above has the following problems. That is, in the frequency calculator 11, the torque voltage reference Vq
* And the excitation voltage reference Vd *, the inverter output frequency ω0 is calculated.
Information on motor constants (not shown) such as the excitation inductance and secondary resistance of the induction motor 3 is used, and errors may occur in the motor constants due to these measurement errors and changes due to temperature, current, and the like. .

Also, due to the influence of a dead time (not shown) for preventing a short circuit due to an operation delay time of the switching element of the inverter circuit 2, the actual applied voltage of the induction motor 3, the torque voltage reference Vq *, and the excitation voltage reference V
An error occurs in d *.

Due to the error, an error also occurs in the calculation of the inverter output frequency ω0, and the calculated value of the inverter output frequency ω0 becomes negative despite the fact that the induction motor 3 is rotating in the positive direction at startup. However, there is a problem that the AC motor 3 rotates in the reverse direction for a short time immediately after the start, or that time is spent for the start, or that the start is impossible in the worst case.

Since the excitation inductance, the motor constant such as the secondary time constant, and the dead time are well known, detailed description thereof will be omitted here.

An object of the present invention is to provide a motor control device capable of starting an AC motor extremely stably even when an error occurs in the calculation of the inverter output frequency.

[0030]

According to a first aspect of the present invention, there is provided an inverter circuit for converting DC power into AC power having a desired voltage and frequency. In a motor control device that supplies AC power to an AC motor and drives the motor at a variable speed, a current flowing through the AC motor is coordinate-transformed based on an output voltage reference phase of an inverter circuit to convert each component current of a torque component current and an excitation component current. Motor current coordinate conversion means, a speed control calculation means for generating a torque reference of the AC motor based on a deviation between the speed reference and the estimated speed of the AC motor, a magnetic flux reference, a torque reference and an estimated speed of the AC motor Vector control means for separating and controlling each component of the torque component current reference and the excitation component current reference based on A slip frequency calculating means for calculating a slip frequency of the AC motor based on the reference, a deviation between the torque component current reference and the torque component current, and a deviation between the excitation component current and the excitation component current, Current control means for generating a torque voltage reference and an excitation voltage reference; frequency calculation means for calculating a frequency of a voltage applied to the AC motor based on the torque voltage reference, the excitation voltage reference, the torque component current and the excitation component current; A voltage phase calculating means for calculating and outputting the output voltage reference phase based on the frequency output from the frequency calculating means, and calculating and outputting the estimated speed based on the frequency and the slip frequency output from the frequency calculating means. And a lower limit for the frequency output from the frequency calculating means so that the frequency does not fall below a predetermined level. And a lower limit means for providing bets.

Therefore, in the motor control device according to the first aspect of the present invention, a lower limit is given to the frequency output from the frequency calculating means so that the inverter output frequency does not drop below a predetermined level. ,
In the low-speed range, a frequency equal to or higher than a predetermined level can be supplied to the AC motor regardless of the calculated value of the inverter output frequency. And the AC motor can be started very stably.

According to a second aspect of the present invention, in the motor control device according to the first aspect of the present invention, the lower limit means includes a frequency lower limit limit according to the polarity of the speed reference of the AC motor. The range is determined.

Therefore, in the motor control device according to the present invention, the range of the lower limit of the frequency by the lower limit means is determined in accordance with the polarity of the speed reference of the AC motor. Since a voltage having a frequency having the same polarity as the speed reference is applied, the AC motor can be started very stably in both the positive and negative rotation directions.

According to a third aspect of the present invention, in the motor control device according to the second aspect,
As the lower limit means, when the polarity of the speed reference of the AC motor is changed, the AC motor is not operated for a predetermined time after the change of the polarity.

Therefore, in the motor control device according to the invention, when the polarity of the speed reference of the AC motor changes, the lower limit means is not operated for a predetermined time from the time when the polarity changes. By doing so, the AC motor can be started very stably, and at the same time, there is a change in the speed reference accompanied by a polarity change,
Even if there is a delay in following the speed of the AC motor, the AC motor can be operated extremely stably.

On the other hand, according to a fourth aspect of the present invention, in the motor control device according to the first or second aspect, the lower limit means is operated for a predetermined time from the start of the AC motor. Like that.

Therefore, in the motor control device according to the present invention, the lower limit means is operated for a predetermined time from the start of the AC motor, so that the AC motor has a lower limit for a predetermined time after the start. Since a voltage having a frequency in one direction of the normal rotation direction or the reverse rotation direction determined by the limit means is applied, the AC motor can be started very stably.

According to a fifth aspect of the present invention, in the motor control device according to the second aspect of the present invention, when the polarity of the speed reference of the AC motor changes, the lower limit means changes the polarity. The operation is not performed from the time of the change until the estimated speed falls within the predetermined range.

Therefore, in the motor control device according to the present invention, when the polarity of the speed reference of the AC motor changes, the time from when the polarity changes to when the estimated speed becomes a predetermined range is obtained. By not operating the lower limit means, it is possible to start the AC motor extremely stably, and at the same time, there is a change in the speed reference accompanied by a polarity change, and even when there is a delay in following the AC motor speed. Thus, the AC motor can be operated extremely stably.

According to a sixth aspect of the present invention, in the motor control device according to the first or second aspect of the present invention, as the lower limit means, the estimated speed is set to a predetermined level from the start of the AC motor. It works only until it reaches.

Therefore, in the motor control device according to the present invention, the lower limit means is operated only from the start of the AC motor until the estimated speed reaches a predetermined level. Until is equal to or more than a predetermined value, the AC motor is applied with a voltage having a frequency in one direction of the normal rotation direction or the reverse rotation direction determined by the lower limit means, so that the AC motor can be started extremely stably. .

According to a seventh aspect of the present invention, in the electric motor control device according to any one of the first to sixth aspects, the estimated speed calculating means is replaced by a frequency calculating means. Is input as it is, and to the voltage phase calculating means, the frequency given the lower limit, which is the output of the lower limit means, is input.

Therefore, in the motor control device according to the present invention, the frequency which is the output of the frequency calculating means is directly input to the estimated speed calculating means, and the lower limit means is input to the voltage phase calculating means. By inputting the frequency with the lower limit, which is the output, the AC motor can be started very stably, and at the same time, use the frequency, which is the output of the frequency calculating means before the limit processing, for calculating the estimated speed. Thus, it is possible to obtain a more accurate estimation speed than in the case of the invention corresponding to claim 1.

[0044]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a lower limit is given to a frequency output from a frequency calculating means so that an inverter output frequency does not drop below a predetermined level.

That is, in the low speed region, a frequency higher than a predetermined level is supplied to the AC motor regardless of the calculated value of the inverter output frequency, so that the AC motor is not affected by the calculation error by the frequency calculation means. This realizes a very stable start-up.

Hereinafter, an embodiment of the present invention based on the above-described concept will be described in detail with reference to the drawings.

(First Embodiment) FIG. 1 is a block diagram showing a configuration example of a motor control device according to the present embodiment. The same parts as those in FIG. Here, only the different parts will be described.

That is, the motor control device according to the present embodiment has a configuration in which a lower limit calculator 15 is added to the output stage of the frequency calculator 11 in FIG.

The lower limit calculator 15 calculates and gives a lower limit ω1 to the frequency ω0 output from the frequency calculator 11 so that the frequency does not fall below a predetermined level.

FIG. 2 is a characteristic diagram showing an example of the calculation contents of the lower limit calculator 15.

In the example of FIG. 2, it is assumed that the speed reference ωr * of the induction motor 3 has only a positive polarity (forward direction).

Next, the operation of the electric motor control device according to the present embodiment configured as described above will be described.

The description of the operation of the same parts as in FIG. 15 is omitted, and only the operation of the different parts will be described here.

In FIG. 1, for example, when a positive speed reference ωr * is inputted based on an operation command (not shown) and the start is started, the frequency ω0 output from the frequency calculator 11 is reduced due to the above-mentioned error. Even if it becomes negative, the inverter output frequency ω
1 does not fall below a predetermined level, and a voltage having a frequency in the normal rotation direction is always applied to the induction motor 3.

Thus, a very smooth starting characteristic of the induction motor 3 can be obtained.

That is, in the low-speed region, a frequency higher than a predetermined level can be supplied to the induction motor 3 irrespective of the calculated value of the inverter output frequency. However, the influence of the calculation error is eliminated, and the induction motor 3 can be started very stably.

The same applies to the case of negative polarity (reverse direction).

As described above, in the motor control device according to the present embodiment, the lower limit is given to the frequency output from the frequency calculator 11 so that the inverter output frequency does not drop below the predetermined level. Since a voltage having a frequency in the forward rotation direction is always applied to the induction motor 3, it is possible to obtain a very smooth starting characteristic of the induction motor 3.

(Second Embodiment) FIG. 3 is a block diagram showing a configuration example of a motor control device according to the present embodiment. The same parts as those in FIG. Here, only the different parts will be described.

That is, the motor control device according to the present embodiment, as shown in FIG. 3, omits the lower limit calculator 15 in FIG. 1 and newly includes a lower limit calculator 16 in place of this. It has a configuration. The lower limit calculator 16 calculates and gives a lower limit ω1 to the frequency ω0 output from the frequency calculator 11 so that the frequency does not fall below a predetermined level.

The lower limit calculator 16 determines the range of the lower limit ω1 of the frequency according to the polarity of the speed reference ωr * of the induction motor 3.

FIG. 4 is a block diagram showing a configuration example of the lower limit calculator 16.

As shown in FIG. 4, the lower limit calculator 1
Reference numeral 6 denotes limit calculators 17 and 18 that receive the frequency ω0 output from the frequency calculator 11 as inputs, and a polarity that receives the speed reference ωr * of the induction motor 3 and determines the polarity of the speed reference ωr *. It comprises decision units 19 and 20, and an RS flip-flop 21 which uses the outputs of the polarity decision units 19 and 20 as a set input and a reset input. FIG. 5 is a characteristic diagram showing an example of the calculation contents of the limit calculators 17 and 18.

Next, the operation of the motor control device according to the present embodiment configured as described above will be described.

The description of the operation of the same parts as in FIG. 1 is omitted, and only the operation of the different parts will be described here.

In FIG. 3, a lower limit calculator 16 calculates a lower limit ω1 for a frequency ω0 output from the frequency calculator 11 so that the frequency does not fall below a predetermined level.

In this case, in the lower limit calculator 16,
The range of the lower limit ω1 of the frequency is determined according to the polarity of the speed reference ωr * of the induction motor 3.

That is, in the example of FIG. 4, when the speed reference ωr * of the induction motor 3 has a positive polarity, the output of the RS flip-flop 21 becomes Q = 1, Q = 0, and the input signal ω0
Becomes an output signal ω1 through the limit calculator 17.

When the speed reference ωr * of the induction motor 3 has a negative polarity, the output of the RS flip-flop 21 is Q =
0, Q = 1, and the input signal ω0 becomes the output signal ω1 through the limit calculator 18.

That is, the speed reference ωr * of the induction motor 3
Is positive, inverter output frequency ω1 is limited to positive polarity, and when speed reference ωr * of induction motor 3 is negative, inverter output frequency ω1 is limited to negative polarity.

Thus, a very smooth starting characteristic of the induction motor 3 can be obtained.

That is, since a voltage having a frequency having the same polarity as the speed reference ωr * is applied to the induction motor 3,
Extremely smooth starting characteristics can be obtained in both positive and negative rotation directions.

As described above, in the motor control device according to the present embodiment, the range of the lower limit ω1 of the frequency in the lower limit calculator 16 is determined according to the polarity of the speed reference ωr * of the induction motor 3. So
Since a voltage having the same polarity as the speed reference ωr * is applied to the induction motor 3, it is possible to obtain a very smooth start-up characteristic of the induction motor 3 in both the positive and negative rotation directions.

(Third Embodiment) FIG. 6 shows a lower limit calculator 1 in a motor control device according to the present embodiment.
6 is a block diagram showing an example of the configuration of FIG. 6, in which the same components as those in FIG. 4 are denoted by the same reference numerals, and the description thereof will be omitted;

That is, as shown in FIG. 6, the lower limit calculator 16 according to the present embodiment newly receives the outputs of the polarity determiners 19 and 20 in FIG. ON delay units 22 and 23 whose output signals become 1 after a predetermined time from the start, an exclusive OR operation unit 24 which receives the output of the polarity determination unit 19 and the output of the ON delay unit 22 as inputs, and a polarity determination unit 20 Output and ON delay 2
3 and an exclusive-OR operator 25 having the outputs of the exclusive-OR operators 24 and 25 as inputs. As described above, when the polarity of the speed reference ωr * of the induction motor 3 changes, the lower limit calculator 16 is not operated for a predetermined time from the time when the polarity changes.

FIG. 7 is a characteristic diagram showing an example of calculation contents (time axis operation example) of the lower limit calculator 16.

Next, the operation of the motor control device according to the present embodiment configured as described above will be described.

The description of the operation of the same parts as in FIG. 4 is omitted, and only the operation of the different parts will be described here.

In FIG. 6, the speed reference ω of the induction motor 3
When the polarity of r * changes, the lower limit calculator 16 does not operate for a predetermined time from the time when the polarity changes.

That is, in the example of FIG. 6, as shown in FIG. 7, at time t = t1, the speed reference ω of the induction motor 3
When r * changes from the positive polarity to the negative polarity, the ON delay unit 23
The output of the logical sum operator 26 is 1 for the delay operation time Δt1 of
As a result, the output signal ω1 becomes equal to the input signal ω0, and the limit operation is canceled during the time Δt1.

This is because when there is a change in the speed reference ωr * of the induction motor 3 accompanied by a polarity change, the speed reference ωr *
In the case where there is a delay in following the speed of the induction motor 3 due to a large moment of inertia or the like with respect to the change of, the limit output units 17 and 18 can prevent the inverter output frequency ω1 from becoming discontinuous. .

The above is based on the speed reference ω of the induction motor 3.
The same applies when r * changes from negative to positive.

As a result, a very smooth start-up characteristic of the induction motor 3 is obtained, and at the same time, the speed reference ωr * of the induction motor 3 changes with a change in polarity, and there is a delay in following the speed of the induction motor 3. Even in this case, extremely smooth operation characteristics of the induction motor 3 can be obtained.

As described above, in the motor control device according to the present embodiment, when the polarity of the speed reference of the induction motor 3 changes, the lower limit calculator 16 operates for a predetermined time from the time when the polarity changes. As a result, extremely smooth start-up characteristics of the induction motor 3 can be obtained, and at the same time, there is a change in the speed reference ωr * of the induction motor 3 accompanied by a change in polarity. Even in some cases, it is possible to obtain extremely smooth operating characteristics of the induction motor 3. (Fourth Embodiment) FIG. 8 is a block diagram showing a configuration example of a lower limit calculator 15 in a motor control device according to the present embodiment, and the same parts as those in FIG. The description is omitted, and only different parts will be described here.

That is, as shown in FIG. 8, the lower limit calculator 15 according to the present embodiment has a configuration in which an on delay unit 27 for inputting a start command of the induction motor 3 is newly added to FIG. And As described above, only for a predetermined time from the start of the induction motor 3,
The lower limit calculator 15 is operated.

Next, the operation of the motor control device according to the present embodiment configured as described above will be described.

The description of the operation of the same parts as in FIGS. 1 and 2 will be omitted, and only the operation of the different parts will be described here.

That is, in the example of FIG. 8, at time t = t2, the limit processing is performed by the lower limit calculator 15 during the operation time Δt2 of the ON delay device 27 after the start command of the induction motor 3 is input. The signal is output as ω1, and then ω1 = ω0, and the operation is performed without limit processing.

Although the present embodiment has been described based on the first embodiment, the present invention is not limited to this, and may be performed based on the second embodiment.

As a result, for a predetermined time after the induction motor 3 is started, a voltage having a frequency in one direction in the normal rotation direction or the reverse rotation direction determined by the lower limit calculator 15 is applied to the induction motor 3. Extremely smooth starting characteristics of the electric motor 3 can be obtained.

As described above, in the motor control device according to the present embodiment, the lower limit calculator 15 is operated only for a predetermined time from the start of the induction motor 3, so that the predetermined time after the start is Since a voltage having a frequency in one direction in the forward rotation direction or the reverse rotation direction determined by the lower limit calculator 15 is applied to the induction motor 3, it is possible to obtain a very smooth start-up characteristic of the induction motor 3.

(Fifth Embodiment) FIG. 9 is a block diagram showing a configuration example of a motor control device according to the present embodiment. The same parts as those in FIG. Here, only the different parts will be described.

That is, as shown in FIG. 9, the motor control device according to the present embodiment is provided with a lower limit calculator 28 instead of the lower limit calculator 15 shown in FIG. It has a configuration. The lower limit calculator 28 calculates and gives a lower limit ω1 to the frequency ω0 output from the frequency calculator 11 so that the frequency does not fall below a predetermined level.

When the polarity of the speed reference ωr * of the induction motor 3 changes, the lower limit calculation unit 28
No operation is performed from the time when the polarity changes to the time when the estimated speed ωr falls within the predetermined range.

FIG. 10 is a block diagram showing a configuration example of the lower limit calculator 28. As shown in FIG.

As shown in FIG. 10, the lower limit calculator 28 includes a level determiner 29 for determining that the estimated speed ωr of the induction motor 3 is equal to or higher than a predetermined value, and a A level determiner 30 for determining that the following conditions are satisfied, an exclusive-OR calculator 31 having as inputs the output of the polarity determiner 19 and the output of the level determiner 29,
An exclusive OR operator 32 that receives the output of the polarity determiner 20 and the output of the level determiner 30 as inputs, and an OR operator 33 that receives the outputs of the exclusive OR operators 31 and 32 as inputs.
And a start command of the induction motor 3, and an ON delay unit 34 whose output signal becomes 1 after a predetermined time from when the input signal becomes 1, an output of the OR operation unit 33 and an output of the ON delay unit 34 And an AND operator 35 having the input as an input. As described above, when the polarity of the speed reference ωr * of the induction motor 3 changes, the lower limit calculator 28 is operated from the time when the polarity changes until the estimated speed ωr of the induction motor 3 falls within the predetermined range. I try not to let them.

FIG. 11 is a characteristic diagram showing an example of calculation contents (time axis operation example) of the lower limit calculator 28.

Next, the operation of the motor control device according to the present embodiment configured as described above will be described.

The description of the operation of the same parts as in FIG. 1 is omitted, and only the operation of the different parts will be described here.

In FIG. 9, the speed reference ω of the induction motor 3
When the polarity of r * changes, the lower limit calculator 28 does not operate from the time when the polarity changes until the estimated speed ωr of the induction motor 3 falls within the predetermined range.

That is, in the example of FIG. 10, as shown in FIG. 11, after the start command of the induction motor 3 is input, the operation is started and the delay operation of the ON delay unit 34 is completed, and then the time t =
At t3, after the speed reference ωr * of the induction motor 3 changes from the positive polarity to the negative polarity, the estimated speed ωr of the induction motor 3 is changed.
Only until the output of the level judgment unit 30 becomes 1 and the output of the OR operation unit 33 becomes 1 and the output signal ω
1 = input signal ω0, and the limit operation is canceled during the period from t = t3 to t4.

This is because when the speed reference ωr * of the induction motor 3 changes with the polarity change, the speed reference ωr *
In the case where there is a delay in following the speed of the induction motor 3 due to a large moment of inertia or the like with respect to the change of, the limit output units 17 and 18 can prevent the inverter output frequency ω1 from becoming discontinuous. .

The above is based on the speed reference ω of the induction motor 3.
The same applies when r * changes from negative to positive.

Further, the criterion value a of the level determinator 29 and the criterion value -b of the level determinator 30 may be changed every moment.

As a result, a very smooth start-up characteristic of the induction motor 3 is obtained, and at the same time, the speed reference ωr * of the induction motor 3 is changed with a change in polarity, and there is a delay in following the speed of the induction motor 3. Even in this case, extremely smooth operation characteristics of the induction motor 3 can be obtained.

As described above, in the motor control device according to the present embodiment, when the polarity of the speed reference ωr * of the induction motor 3 changes, the estimated speed ωr of the induction motor 3 is changed from the time when the polarity changes. Until it reaches the predetermined range,
Since the lower limit calculator 28 is not operated, very smooth start-up characteristics of the induction motor 3 can be obtained, and at the same time, there is a change in the speed reference ωr * of the induction motor 3 accompanied by a polarity change, and the induction motor 3 Even when there is a delay in following the speed 3, the extremely smooth operation characteristics of the induction motor 3 can be obtained. (Sixth Embodiment) FIG. 12 is a block diagram showing a configuration example of a motor control device according to the present embodiment. The same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted. Now, only the different parts will be described.

That is, as shown in FIG. 12, the motor control device according to the present embodiment has a lower limit calculator 15 instead of the lower limit calculator 15 shown in FIG. 1, and a new lower limit calculator 36 is newly provided. It has a configuration. The lower limit calculator 36 calculates the lower limit ω1 for the frequency ω0 output from the frequency calculator 11 so that the frequency does not fall below a predetermined level.

The lower limit computing unit 36 calculates the estimated speed ωr of the induction motor 3 from the start of the induction motor 3.
Operates only until the predetermined level is reached.

FIG. 13 is a block diagram showing an example of the configuration of the lower limit computing unit 36. The same parts as those in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted. Only different parts will be described here.

That is, as shown in FIG. 13, the lower limit calculator 36 newly sets a level determiner 37 for determining that the estimated speed ωr of the induction motor 3 is equal to or greater than the determination reference value c in FIG. The configuration is added. Next, the operation of the motor control device according to the present embodiment configured as described above will be described.

The description of the operation of the same parts as in FIGS. 1 and 2 is omitted, and only the operation of the different parts will be described here.

In FIG. 12, the lower limit computing unit 36 operates only from the start of the induction motor 3 until the estimated speed ωr of the induction motor 3 reaches a predetermined level.

That is, in the example of FIG. 12, as shown in FIG. 13, the estimated speed ωr of the induction motor 3 is
Until the value becomes equal to or more than the determination reference value c of 7, the limit operation is performed by the limit calculator 36, after which the limit operation is released.

Although the present embodiment has been described based on the first embodiment, the present invention is not limited to this, and may be performed based on the second embodiment.

As a result, until the estimated speed ωr becomes equal to or higher than the predetermined value after the induction motor 3 is started, the induction motor 3
Is applied with a voltage having a frequency in one direction of the normal rotation direction or the reverse rotation direction determined by the lower limit calculator 36, so that a very smooth starting characteristic of the induction motor 3 can be obtained.

As described above, in the motor control device according to the present embodiment, the estimated speed ωr
The lower limit computing unit 36 is operated only until the motor reaches a predetermined level, so that the induction motor 3 has the induction motor 3 rotate the forward direction or the reverse rotation determined by the lower limit computing unit 15 for a predetermined time after starting. Since a voltage having a frequency in one direction is applied, it is possible to obtain an extremely smooth startup characteristic of the induction motor 3.

(Seventh Embodiment) FIG. 14 is a block diagram showing a configuration example of a motor control device according to the present embodiment. The same parts as those in FIG. 1 are denoted by the same reference numerals and description thereof is omitted. Here, only the different parts will be described.

That is, in the motor control device according to the present embodiment, as shown in FIG. 14, the frequency ω0 output from the frequency calculator 11 is directly input to the estimated speed calculator 12 in FIG. And the voltage phase calculator 1
For 3, the frequency ω1 to which the lower limit, which is the output of the lower limit calculator 15, is given is input. Next, the operation of the motor control device according to the present embodiment configured as described above will be described.

The description of the operation of the same parts as in FIG. 1 is omitted, and only the operation of the different parts will be described here.

In FIG. 1, the estimated speed ω of the induction motor 3 is
While the output of the lower limit calculator 15 is used as an input of the estimated speed calculator 12 for calculating r, FIG.
4, the output of the frequency calculator 11 (= input of the lower limit calculator 15) is used as an input of the estimated speed calculator 12.

As a result, not only can the smooth start-up characteristic of the induction motor 3 be obtained, but also the frequency ω0 before the limit processing is used in the calculation of the estimated speed ωr of the induction motor 3, thereby obtaining the first embodiment. It is possible to obtain an estimated speed ωr with extremely higher accuracy than in the case of

Although the present embodiment is based on the first embodiment, the present invention is not limited to this, and may be implemented in combination with any of the second to sixth embodiments. And the same effect can be obtained.

As described above, in the motor control device according to the present embodiment, the frequency ω 0 output from the frequency calculator 11 is directly input to the estimated speed calculator 12, and In other words, since the frequency ω1 having the lower limit, which is the output of the lower limit calculator 15, is input, extremely smooth start-up characteristics of the induction motor 3 can be obtained, and at the same time, induction with a change in polarity can be achieved. Even when the speed reference ωr * of the electric motor 3 changes and there is a delay in following the speed of the induction motor 3, the induction motor 3
It is possible to obtain extremely smooth driving characteristics.

[0124]

As described above, according to the motor control device of the present invention, the lower limit is given to the frequency output from the frequency calculating means so that the inverter output frequency does not fall below the predetermined level. Therefore, even if an error occurs in the calculation of the inverter output frequency,
It is possible to start the AC motor very stably (obtain an extremely stable starting characteristic).

[Brief description of the drawings]

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

FIG. 2 is a characteristic diagram showing an example of calculation contents of a lower limit calculator in the motor control device of the first embodiment.

FIG. 3 is a block diagram showing a second embodiment of the motor control device according to the present invention.

FIG. 4 is a block diagram showing a configuration example of a lower limit calculator in the electric motor control device according to the second embodiment;

FIG. 5 is a characteristic diagram showing an example of a calculation content of a limit calculator of a lower limit calculator in the motor control device of the second embodiment.

FIG. 6 is a block diagram showing a configuration example of a lower limit calculator in a motor control device according to a third embodiment of the present invention.

FIG. 7 is a characteristic diagram showing an example of a calculation content of a lower limit calculator in the electric motor control device according to the third embodiment.

FIG. 8 is a block diagram showing a configuration example of a lower limit calculator in a motor control device according to a fourth embodiment of the present invention.

FIG. 9 is a block diagram showing a fifth embodiment of the motor control device according to the present invention.

FIG. 10 is a block diagram showing a configuration example of a lower limit calculator in the motor control device according to the fifth embodiment.

FIG. 11 is a characteristic diagram showing an example of a calculation content (an example of a time axis operation) of a lower limit calculator in the motor control device according to the fifth embodiment.

FIG. 12 is a block diagram showing a sixth embodiment of the motor control device according to the present invention.

FIG. 13 is a block diagram showing a configuration example of a lower limit calculator in the electric motor control device according to the sixth embodiment.

FIG. 14 is a block diagram showing a seventh embodiment of the motor control device according to the present invention.

FIG. 15 is a block diagram showing a configuration example of a conventional motor control device.

16 is a circuit diagram showing a main circuit configuration example of an inverter circuit in the motor control device of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... DC power supply, 2 ... Inverter circuit, 3 ... Induction motor, 4 ... Current detector, 5 ... Motor current coordinate converter, 6 ... Speed controller, 7 ... Vector controller, 8 ... Slip frequency calculator, 9 ... Current controller, 10: Voltage reference coordinate converter, 11: Frequency calculator, 12: Estimated speed calculator, 13: Voltage phase calculator, 14: PWM controller, 15: Lower limit calculator, 16: Lower limit calculation , 17, 18: Limit operator, 19, 20: Polarity determiner, 21: RS flip-flop, 22, 23: ON delayer, 24, 25: Exclusive OR operator, 26: OR operator, 27: ON delay unit, 28: Lower limit operation unit, 29, 30: Level judgment unit, 31, 32: Exclusive OR operation unit, 33: OR operation unit, 34: ON delay unit, 35: AND operation Bowl, 6 ... lower limit calculator, 37 ... level determiner.

Claims (7)

[Claims] 1. An electric motor control device, comprising: an inverter circuit for converting DC power into AC power of a desired voltage and frequency; and supplying the AC power of the inverter circuit to an AC motor and driving the motor at a variable speed. Based on the output voltage reference phase, motor current coordinate conversion means for converting the current flowing in the AC motor into respective component currents of a torque component current and an excitation component current by coordinate conversion, and a speed reference and an estimated speed of the AC motor. A speed control calculating means for generating a torque reference for the AC motor based on the deviation of the AC motor; and a torque component current reference and an excitation component current reference based on the magnetic flux reference, the torque reference and the estimated speed of the AC motor. Vector control means for separating and controlling each component, based on the torque component current reference and the magnetic flux reference,
A slip frequency calculating means for calculating a slip frequency of the AC motor; a deviation between the torque component current reference and the torque component current; and a deviation between the excitation component current and the excitation component current, Current control means for generating a torque voltage reference and an excitation voltage reference; calculating a frequency of a voltage applied to the AC motor based on the torque voltage reference, the excitation voltage reference, the torque component current, and the excitation component current A frequency calculating means for calculating, based on a frequency output from the frequency calculating means, a voltage phase calculating means for calculating and outputting the output voltage reference phase; and a frequency output from the frequency calculating means and the slip frequency. Estimated speed calculating means for calculating and outputting the estimated speed, based on the frequency output from the frequency calculating means. , Motor control device characterized in that said frequency is provided with a lower limit means for providing a lower limit so as not to be below a predetermined level. 2. The motor control device according to claim 1, wherein the lower limit means determines a range of a lower limit of a frequency according to a polarity of a speed reference of the AC motor. Motor control device. 3. The motor control device according to claim 2, wherein, when the polarity of the speed reference of the AC motor is changed, the lower limit means is a predetermined time from the time when the polarity is changed. A motor control device characterized in that it is not operated. 4. The electric motor control device according to claim 1, wherein the lower limit means is operated only for a predetermined time from the start of the AC motor. Control device. 5. The motor control device according to claim 2, wherein, when the polarity of the speed reference of the AC motor is changed, the estimated speed is changed from the time when the polarity is changed. An electric motor control device, wherein the motor control device is not operated until a predetermined range is reached. 6. The electric motor control device according to claim 1, wherein the lower limit means is operated only from a time when the AC motor is started until the estimated speed reaches a predetermined level. An electric motor control device, characterized in that: 7. The method according to claim 1, wherein
In the motor control device described in the paragraph, for the estimated speed calculation means, the frequency which is the output of the frequency calculation means is directly input, and for the voltage phase calculation means, the output of the lower limit means is used. A motor control device characterized in that a frequency given a certain lower limit is input.