JPH0974800A - Control apparatus for ac motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a control apparatus whose efficiency can be increased and whose control stability can be enhanced by a method wherein, when an AC motor is operated up to a high-speed region, an exciting current which is more than required is not made to flow in order to prevent the control of the AC motor from becoming impossible. SOLUTION: In order to prevent a d-axis current from becoming unable to follow a command value in a transient state, the control operation on the side of a d-shaft is performed preferentially. That is to say, a voltage-vector- length maximum-value setter 51 outputs an inverter-output-voltage-vector-length maximum value |v*IMAX| on the basis of an inverter DC voltage vDC. A q-shaft- voltage maximum-value setter 52 outputs a second q-shaft-voltage command value vq ** on the basis of a d-shaft-voltage command value vd * from a d-q-shaft- current control circuit 17. A PI controller 54 outputs a d-shaft-current command value id * to the d-q-shaft-current control circuit 17 in such a way that a q-shaft- voltage command value vq * does not exceed the command value vq **.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC motor control device, and more particularly to a technique for improving operating characteristics in a high rotation speed range.

[0002]

2. Description of the Related Art An AC electric motor produces a speed electromotive force when it is operated, and if the magnetic flux is constant, the magnitude of the speed electromotive force is proportional to the rotational speed. Therefore, there is a rotational speed at which the value of the speed electromotive force exceeds the value of the voltage that can be applied if the magnetic flux is constant. Below this number of revolutions is generally read as the torque region, and above is read as the constant output region. In the constant torque range, the magnetic flux only needs to be kept constant, so control is relatively simple. In the constant output region, the magnetic flux is controlled in inverse proportion to the number of revolutions in a synchronous motor or induction motor that can control the magnetic flux, and in the permanent magnet motor in which the magnetic flux cannot be controlled, the inductance of the motor winding is reduced. To increase the voltage drop due to.

The current control of these AC motors is often performed by dq axis current control. In the past, in order to control the instantaneous value of the AC current to follow the AC command value as well, P
The I controller was also operated by alternating current, but the operating frequency of the electric motor could not be increased because of lack of followability at high frequency. However, the dq axis current control has made it possible to expand the operating range of the electric motor.

However, there is a point that it is hard to say that the electric power of the electric motor is fully exhibited by the dq axis current control. This will be described based on the conventional example of the controller for the permanent magnet motor shown in FIG. In FIG. 4, 1 is a DC power source, 2
Is a capacitor, 3 is an inverter, 4 is a permanent magnet motor,
Reference numeral 5 is a pulse encoder, and 6U and 6W are current detectors such as Hall CT mounted on the U-phase and W-phase electric wires of the permanent magnet motor. The DC power supply 1 is of various types such as a case where a battery is used and a case where it is composed of an AC power supply and a rectifier.
The inverter 3 is controlled by the control circuit 10 and applies a variable voltage variable frequency voltage to the permanent magnet motor 4.

The control circuit 10 receives the output signal of the pulse encoder 5 and outputs the rotation information such as the rotation speed ω _r and the rotation angle θ _{r of the} permanent magnet motor 4 and the current detectors 6U and 6W. receiving the output signal, the current detection signal i _U, a current detecting circuit 12 for outputting a i _W, the current detection signal based on the rotation angle theta _r of the permanent magnet motor 4 i _U, from UVW stationary coordinate system relative to i _W UVW / d to obtain a current component i _{d in} phase with the magnetic flux produced by the permanent magnet and a current component i _{q in the} direction perpendicular to the magnetic flux produced by the permanent magnet by performing conversion into a dq rotational coordinate system synchronized with the rotation of the magnetic poles of the electric motor. -Q coordinate conversion circuit 1
3, the voltage detector 14 for detecting the _DC voltage v _DC of the inverter 3, the rotational speed ω _r of the permanent magnet motor 4 and the DC voltage v _{DC of the} inverter should be applied to the permanent magnet motor 4. d that outputs the command value i _d ^* of the d-axis current component
Similarly to the shaft current commander 15, the rotation speed ω of the permanent magnet motor
The maximum value i of the q-axis current component that can be passed through the permanent magnet motor 4 based on _r and the DC voltage v _DC of the inverter 3
_{Find qmax} , and use that value to give q given by a circuit not shown.
A q-axis current command value limit circuit 16 that outputs a q-axis current command value i _q ^* capable of flowing to the permanent magnet motor 4 by limiting the axis current command value i _q ^** , and a d-axis current command value i _d. ^*
And d-q axis current control circuit 1 which outputs voltage command values v _d ^* and v _q ^* on the d-q axes so that the current detections _id and _iq follow the q-axis current command value i _q ^*.
7, the voltage command values v _d ^* and v _q ^* DC section voltage v _DC
By dividing the voltage command values v _d ^* and v _q ^* by the control rate α _d
^{Based on the} dividers 18d and 18q for converting to ^* and α _q ^* , and the control ratios α _d ^* and α _q ^* based on the rotation angle θ _r of the permanent magnet motor 4, from the dq rotating coordinate system to the UVW stationary coordinate system. control rate alpha _U ^* performs conversion to, alpha _V ^*, the d-q / UVW coordinate converting circuit 19 for outputting alpha _W ^*, the control factor ^{_{α U *, α V *,}} PWM enter the alpha _W ^* And a PWM control circuit 20 that outputs a signal.

Although a detailed diagram of the PWM control circuit 20 is omitted, this is a three-phase generator in which a triangular wave generator, an output triangular wave of the triangular wave generator, and control rates α _U ^* , α _V ^* , and α _W ^* are compared. , A polarity inversion circuit that obtains the respective polarity inversion signals of the PWM signals, and a dead time circuit that delays a predetermined time when the comparator output and the polarity inversion circuit output change from the OFF logic to the ON logic. And is a very general PWM control circuit. The dividers 18d and 18q described above keep the proportional relationship between the amplitude of the output triangular wave of the triangular wave generator and the magnitude of the inverter DC section voltage v _DC constant, regardless of the variation of the inverter DC section voltage v _DC. It plays a role of keeping the PI gain of the q-axis current control circuit 17 constant.

The six PWM signals output from the PWM control circuit are given to the inverter 3 via a gate circuit (not shown ^), and the permanent magnets are supplied to the d-axis current command value i _d ^* and the q-axis current command value i _q ^*. The d-axis current and the q-axis current of the electric motor 4 are controlled so as to follow. Since the d-axis and the magnetic flux direction of the permanent magnet are aligned and the q-axis is oriented in the direction perpendicular to the magnetic flux of the permanent magnet, the torque generated by the permanent magnet is determined only by the q-axis current. For this reason, the q-axis current is also referred to as the torque component current. On the other hand, the d-axis current is irrelevant to the torque and is controlled to enable the operation in the constant output region. For this reason, the d-axis current is also called an excitation current.

How much i _d has to flow when a certain torque current i _q flows through the permanent magnet motor in the constant output region will be described with reference to the vector diagrams of FIGS. 5 and 6.
However, in FIGS. 5 and 6, for simplicity, the permanent magnet motor 4 is used.
The resistance of the winding wire is ignored, and only the inductance L is drawn. FIG. 5 shows no load, that is, the torque current i _q is zero. When the magnetic flux from the permanent magnet is φ _m , a velocity electromotive force of E _m = ω _r · Φ _m is generated. The arc in FIG. 5 is an arc having a radius of the maximum voltage V _IMAX that can be output by the inverter 3, and the inverter 3 can output within this arc. Therefore, if the induced voltage is within the arc, it is not necessary to flow the exciting current i _d . In the constant output area, there is no burden Senebaranara in the voltage drop ω _r L · i _d due to the inductance and the difference voltage is greater is more of the street speed electromotive force of the figure. Therefore, at no load, i _d = (V _IMAX −E _m ) / ω _r L = (V _IMAX −ω _r · Φ
A d-axis current of _m ) / ω _r L is required. In the constant output region (V _IMAX −ω
_{Since r} · Φ _m ) <0, the value of i _d is negative. This equation shows that the higher the rotational speed, the more the required i _d .

FIG. 6 shows a case in which a positive torque current i _q is flowing. The torque component current i _q causes a voltage drop of ω _r L · i _q in the negative direction of the d-axis as shown in the figure. In this case as well, the output voltage of the inverter 3 must be within the arc of the radius V _IMAX . In this case, the vector of the vector and the inverter output voltage V _IMAX of torque current i _q and the exciting component current impedance drop of the vector sum ie total current i _t of i _d ω _r L · i _t of the vector and the speed electromotive force E _m Since a triangle is formed by, from the cosine theorem,

[0010]

[Equation 1] D-axis current is required. That is, q
When the axial current becomes large, a large i _d is required according to the above formula. Conversely, it suffices to let i _d to satisfy the above equation, and i _d should be controlled according to the value of the rotation speed and the torque current i _q .

However, in the actual controller of the permanent magnet motor, i _d of a value much larger than the value satisfying the above relation must be flowed. This is because the above equation is a relation in the steady state, and a voltage margin larger than those shown in FIGS. 5 and 6 may be required during a transition in which the values of i _d and i _q are changed, and This is because if the voltage is transiently insufficient, control may be lost.
Once the control is lost, control cannot be restored unless either the rotational speed or the torque current command is significantly reduced.

This will be described with reference to FIG. FIG. 7 shows d-
3 is an example of a configuration of a q-axis current control circuit 17. 7, 31d and 31q are subtractors, 32d and 32q are PI control circuits, 33d and 33q are multipliers, 34 is a subtractor, and 35
Is an adder, and 36 is the rotation speed ω _r of the permanent magnet motor, and is multiplied by the gain L of the inductance of the permanent magnet to obtain ω _r
Similarly, a multiplier 37 for outputting L is a multiplier for inputting the rotational speed ω _r of the permanent magnet motor and multiplying the gain Φ _{m of the} magnetic flux produced by the permanent magnet, and outputting ω _r · Φ _m . Subtractor 31d
The current detection i _d is subtracted from the excitation current command i _d ^* at
The deviation is PI-controlled by the PI controller 32d. The output of the PI controller 32d is subtracted from the output of the multiplier 33q by the subtractor 34 to obtain a d-axis voltage command v _d ^* . q-axis side, similarly, the subtracter 32q, PI controller 32q, through the adder 35, is a q-axis voltage command v _q ^*. The adder 35 adds the output of the multiplier 37d and the output of the multiplier 37d to the output of the PI controller 32q. Multipliers 33d, 33
q is the current detection i _d , i _q and the output ω of the multiplier 36
multiplied by the _{r L, ω r L · i} d, and outputs the ω _r L · i _q.

The voltage-current equation of a permanent magnet motor is

[0014]

[Equation 2] , The subtractor 34 and the adder 35 respectively calculate the second term and the following terms on the right side of the above two equations from the PI controller 32.
It is added to the outputs of d and 32q. By adding or subtracting the second term on the right side of each of the above two equations to the PI controller output, it is possible to remove the influence of the currents flowing in the orthogonal d-q axes on the orthogonal axes. In addition, by adding the third term on the right side of the equation on the q-axis side, it is possible to remove the influence of the change in speed electromotive force due to the rotation speed. As a result, the PI controllers 32d, 32
It suffices for q to bear only the resistance component of its own phase, the inductance component, and the error component of the setting constant. The current control circuit having the above-described configuration enables good current control in the constant torque region.

Next, in the constant output region, the torque current command i _q
Consider the case where a large amplitude step change is applied to ^* and the value is rapidly increased. Since it is in the constant output region, the speed electromotive force E _m = ω _r · Φ
_m has already exceeded the magnitude V _IMAX of the maximum voltage vector that can be output by the inverter. Therefore, the negative excitation current i _d is passed to reduce the q-axis component voltage. As the value of i _d at this time, the given torque current command i _q ^*
Even when a torque current commensurate with the value after the step change of flows, the inverter voltage is a current that can be output. That is, even if the current corresponding to the command value after the step change flows, the vector sum of the q-axis component voltage and the d-axis component voltage, that is, the magnitude V ₁ of the inverter output voltage vector is a value slightly lower than V _{IMAX in} the steady state. Suppose Here, when the torque current command i _q ^* rapidly increases in a large amplitude step, the output of the q-axis PI controller 32q increases to the maximum value, and the q-axis component voltage command value v _q ^* has the maximum value V. _It exceeds _IMAX . However, since the inverter cannot actually output a voltage higher than the maximum value V _IMAX , i _q
The increase in is slow. The torque current i _q is the command value i
_{When q} ^* is reached, the output of the q-axis PI controller 32q decreases, and the magnitude of the output voltage command value as a vector can be returned to a value equal to or lower than the maximum value V _IMAX . However, i _q is the command value i
If it does not reach _q ^* , the output of the PI controller 32q continues to output the maximum value, and the control becomes impossible. Moreover, by the fact itself that the output of the PI controller 32q is outputting the maximum value i _q in an attempt to rapidly increase, i _q is the less likely to follow the command value i _q ^*.

This will be described with reference to the vector diagram of FIG. FIG.
In the above, v _q1 ^* and v _d1 ^* are dq axis voltage command component vectors when the value i _q1 ^* before the step change of the torque current command, v _t1 ^* is a composite vector thereof, and the values are actually output by the inverter. _Is equal to the vector of the voltage being applied, v _t1 . The q-axis voltage command value is v _q2 ^* at some point after the torque current command has increased from i _q1 ^* to i _q2 ^* . Assuming that the d-axis voltage command value is the same value v _d1 ^* as before, the vector sum of these is v _t2 ^* , which exceeds the range that the inverter can output. The voltage vector actually output is v on the arc.
_t2 . Therefore, the d- and q-axis voltage components actually output are v _d2 and v _q2 . The magnitude of the d-axis voltage component v _d2 has decreased. A decrease in the d-axis component voltage promotes a decrease in the exciting current component i _d , and a decrease in the exciting current component i _d leads to a decrease in the voltage drop due to the exciting current with respect to the speed electromotive force on the q-axis. That is, it works in the direction of hindering the increase of the q-axis current.
Since the d-axis current has decreased, the PI controller 32d on the d-axis side operates and v _d ^* is increased to restore the d-axis current, but the output of the PI controller 32q on the q-axis side outputs the maximum value. Since v _q2 ^* has velocity electromotive force added to it, its vector length is much larger than the vector length of v _d ^* . As a result, even if the PI controller 32d on the d-axis side saturates, it may not be possible to have a vector relationship that allows a necessary d-axis current to flow. In such a case, both controllers are saturated. Fall into the situation of doing.

Returning to FIG. 4, in order to avoid such a situation, it is necessary to flow a negative exciting current sufficient to secure a sufficient voltage margin even in a transient state. Therefore, the d-axis current commander 15 is sufficient even when the torque current command is maximum, and i _d ^* of a magnitude sufficient for stable control even when the torque current command changes suddenly is the rotation speed. It is given according to the DC voltage. Thus, when the output enable maximum current of the inverter is assumed to be i _tmax, the q-axis in the ^{_{(i tmax 2 -i d * 2}} ) 1/2 ( herein, can not be used to route symbol, hereinafter, this So the square root is 1/2
Expressed as a power index. ) The above torque current cannot be applied. That is, the torque that can be generated at the constant output is reduced by the amount that i _d ^* is increased. This is given by the q-axis current command value limit circuit 16.

[0018]

Therefore, the rotational speed-torque curve of the permanent magnet motor 4 becomes as shown in FIG. The dotted line portion is the rotational speed-torque curve that can be output if the steady state can be reached, and the solid line portion is the rotational speed-torque curve that can be output when considering the transient state. The constant torque region is narrowed by sufficiently flowing i _d ^* , and the torque in the constant output region is limited. Also,
Since the torque cannot be generated as the rotation speed becomes higher,
The operating frequency range that can be actually used is also narrow. Furthermore, since the exciting current is passed to the side, the efficiency is lowered.

According to the present invention, the minimum required exciting current is supplied in the steady state, and when the exciting current is transiently required to be increased, the exciting current amount is automatically controlled. An object of the present invention is to provide an AC motor control device capable of increasing the output capacity of an AC motor, expanding the operating frequency range, improving efficiency, and improving the stability of control in a constant output range without falling into control failure.

[0020]

As a means for solving the above-mentioned problems, the invention according to claim 1 is directed to a current flowing from an electric power converter to an AC electric motor in a magnetic flux direction based on a magnetic flux direction of the AC electric motor. Q perpendicular to the parallel d-axis and the magnetic flux direction
Component i _d on d-q-axis coordinate consisting of a shaft, is detected as i _q, such that q-axis current command value is created based on the given torque current command i _q ^* on the q-axis current i _q to follow The d-axis current command value i _d is created based on the voltage that the power converter can output by controlling the q-axis voltage command value v _q ^*.
* D-axis voltage command value so that the d-axis current i _d to follow the v _d ^*
In the AC motor controller for controlling the output voltage of the power converter based on the q-axis voltage command value v _q ^* and the d-axis voltage command value v _d ^*. The d-axis current command value i _d ^* is controlled based on the related predetermined value | v _IMAX |, the d-axis voltage command value v _d ^*, and the q-axis voltage command value v _q ^*, and the power converter is controlled. The torque current command is limited based on a predetermined value _{│i IMAX} │ related to the current that can be output and the d-axis current command value i _d ^* to obtain a q-axis current command value i _q ^*. And

According to a second aspect of the present invention, in the first aspect of the invention, a predetermined value | v _IMAX | related to the outputtable voltage of the power converter and the d-axis voltage command value v _d ^*
The second q-axis voltage command value v _q ^** is obtained by _q ^** = (| v _IMAX | ² −v _d ^{* 2} ) ^1/2 , and the second q-axis voltage command value v _q ^** and the q The magnitude of the d-axis current command value i _d ^* is controlled based on the comparison with the shaft voltage command value v _q ^*, and a predetermined value | i related to the current that can be output by the power converter.
_A value (| v based on _IMAX | and the d-axis current command value i _d ^*
_IMAX | ² -i _d ^{* 2)} to limit the magnitude of the torque current command by ^1/2 and so that said q-axis voltage command value i _q ^*, it is characterized.

According to a third aspect of the invention, in the invention of the first or second aspect, the power converter is a voltage source PWM.
Using an inverter, the q-axis voltage command value v _q ^* and the d-axis voltage command value v _d ^* and the q-axis voltage v _q actually output from the inverter are detected based on the detection of the DC voltage of the inverter.
And the d-axis voltage v _d are maintained proportionally, PW
The relationship between the control rate of M control and the q-axis voltage command value v _q ^* and the d-axis voltage command value v _d ^* is corrected, and is related to the outputtable voltage of the power converter based on the detection of the DC voltage. It is characterized in that a predetermined value | v _IMAX | is determined.

According to a fourth aspect of the present invention, in the second or third aspect of the invention, the AC motor is an induction motor, and a predetermined value | associated with the outputtable voltage of the power converter.
The q-axis voltage limit value (| v _IMAX | ² −v _d ^{* 2} ) ^1/2 is calculated from v _IMAX | and the d-axis voltage command value v _d ^*, and q is given in proportion to the rotation speed of the induction motor. The axis voltage command value is limited by the q-axis voltage limit value (| v _IMAX | ^2- _vd ^{* 2} ) ^1/2 to obtain the second q-axis voltage command value _vq ^**, and the second q-axis voltage command value _vq ^** is obtained. Based on the comparison between the q-axis voltage command value v _q ^** and the q-axis voltage command value v _q ^* , the d-axis current command value i _d
The magnitude of ^* is controlled, and a predetermined value | i _IMAX | related to the outputtable current of the power converter and the d-axis current command value i _d
^* Value based on the ^{_{(| i IMAX | 2 -i d}} * 2) to limit the magnitude of the torque current command by ^1/2 and the q-axis voltage command value i _q ^*, it is characterized.

As explained in the conventional example, the reason why the control becomes uncontrollable is that while the d-axis current is not able to follow the command value when the operating condition changes, such as an increase in the number of revolutions or a sudden increase in the torque current command, q The output voltage command value on the axis side increases, and a command value greater than the voltage that can be output by the inverter is given as a vector, and as a result, it becomes impossible to secure a d-axis voltage sufficient to control the d-axis current. . In the present invention, the control on the d-axis side is prioritized, and the voltage on the q-axis side is controlled so as not to be out of control. Paying attention to the fact that the maximum value that the inverter can output is the vector sum of the q-axis voltage and the d-axis voltage, the maximum value of the inverter output voltage is defined by the vector length | v _IMAX ^* | As the voltage command value, v _q ^** = (| v
^{_{IMAX * | 2 -v d * 2}} ) 1/2 gives, first q-axis voltage command value of the previous determined as a result of the d-q axis current control v _q ^* are the second voltage command value v _d ^** D-axis current command value i _d ^*
PI is controlled so as to increase in the negative direction. Further, when the maximum output current of the inverter was set to i _tmax ^*, the absolute value of the torque current command value ^{_{i q ** (i imax * 2}} -i d * 2) q -axis side current reference and limit ^1/2 It is given to the current control circuit as i _q ^* .

That is, the torque component current command value i _q ^** , or the p-axis side output v _q ^* of the dq axis current control circuit exceeds the second voltage command value v _q ^{** due} to an increase in the number of revolutions. And q
The d-axis current command value i _d ^* increases in the negative direction by the PI control of the axis-side voltage, and the d-axis current tends to flow more than in the steady state. As a result, the d-axis side output v of the d-q-axis current control circuit
_d ^* increases in the negative direction, and _vq ^** = (| v ^* _IMAX | ^2- v
The second voltage command value v _q ^** determined by _d ^{* 2} ) ^1/2 becomes smaller, and the d-axis current command value i _d ^* is gradually increased in the negative direction. The q-axis side current reference of the q-axis current control d-q axis current control i _q ^* i _q a ^{_{** (i * 2 tmax -i d}} * 2) 1/2
Since the limit value is given by, the absolute value of the q-axis side current reference i _q ^* decreases as i _d ^* increases in the negative direction. The q-axis side output v _q ^* of the d-q axis current control increases once and is saturated when the step amount of the torque current command value i _d ^* is large, but the q-axis current reference i _q.
The absolute value of ^* decreases, so that i _q ^* is i
It becomes equal to _q and the deviation is zero. As a result, v _d ^* is reduced, and the length of the inverter output voltage vector is | v ^*.
_It becomes smaller than _IMAX |, and the d-axis side control of the dq axis current control works effectively. That is, i _d can follow i _d ^* . As a result, the magnitude of the control output v _d ^* on the d-axis side of the d-q axis current control starts to decrease, and
The voltage reference v _q ^** = (| v ^* _IMAX | ^2- _vd ^{* 2} ) ^1/2 turns to increase. Therefore, i _d ^* changes in the positive direction. That is, as the size, i _d ^* gradually decreases. i _q ^* also gradually increases accordingly. Since the length of the inverter output voltage vector is smaller than | v ^* _IMAX |, current control works effectively for both the d-axis and the q-axis.
Both the currents i _d and i _q follow the change in the command value. When i _q ^* finally stabilizes and i _q follows the value, the q-axis side output of the dq axis current control circuit decreases, and the q axis voltage control also decreases i _d ^* .

This reduces the value of v _d ^*
The second voltage command value v _q ^** on the q-axis side increases and returns to the value in the steady state. The magnitude of the d-axis current command value i _d ^* also drops to the minimum current value required in the steady state.

[0027]

1 is a block diagram showing the configuration of an embodiment of the present invention. In FIG. 1, components 1 to 6w and 11 to 14 and 17 to 20 are the same as those in the conventional example of FIG. 51
Is a voltage vector length maximum value setting unit, which receives the inverter DC voltage magnitude v _DC, and outputs an inverter output voltage vector length maximum value | v ^* _IMAX |. The value of | v ^* _IMAX | is set to be slightly smaller than the maximum voltage vector length that the inverter can truly output. 52 is a q-axis voltage maximum value setting device, which is the d-axis side output signal v _d ^* of the d-q axis current control circuit 17 ^.
And the inverter output voltage vector length maximum value | v ^* _IMAX | are input, and the second voltage command value ( _vq ^** = (| v
^* _IMAX | ² −v _d ^{* 2} ) ^1/2 is output. Reference numeral 53 is a subtractor that takes the deviation between the second voltage command value on the q-axis side and the q-axis side output v _q ^* of the dq axis current control circuit 17. Reference numeral 54 denotes a PI which receives the output of the subtractor 53 and controls so that the q-axis side output v _q ^{* of the} dq axis current control circuit 17 does not exceed the q-axis side second voltage command value v _q ^**. It is a controller. PI controller 54
Is given a zero from the constant setter 55 as the maximum value of its output. That is, if _vq ^** > _vq ^* , then P
The output of the I controller 54 is zero and outputs a negative value when v _q ^* exceeds v _q ^** . The output of the PI controller 54 is the d-q current control circuit 1 as the d-axis current command i _d ^*.
Given to 7. The output of the PI controller 54 is also given to the q-axis current maximum value setter 56. q-axis current maximum value setter 5
6 inputs the i _d ^*, based on the i _d ^* and a predetermined maximum output current i ^* _tmax inverter q-axis current maximum value (i * ²
and outputs the _tmax -i _d ^* 2) ^1/2. _{Reference numeral} 57 is a limiter for the torque component current command i _q ^** and the maximum q-axis current value (i ^{* 2} _tmax -i
_{Based on d} ^{* 2} ) ^1/2 , the q-axis side current reference i _q ^* is output to the dq axis current control circuit 17.

Next, the operation of FIG. 1 will be described with reference to FIG. FIG. 2 is an operation waveform diagram of each part when the torque current command is used. FIG. 2 shows the torque current commands i _q ^** , d−q.
D-axis side output signal of the axis current control circuit 17 v _d ^*, q-axis side output signal v _q ^*, the second voltage command value of the q-axis side v _q ^**, d-axis current command i _d ^*, d-axis current i _d, PI control output PI _id of the d-axis current, q-axis side current reference i _q ^*, q-axis current i _q, the control output PI _iq of the q-axis current is shown.

In FIG. 2, at time t _1, a step change from zero to a large current is given to the torque component current command i _q ^** . Since d-q axis current control circuit 17 q-axis side current reference is inputted to the i _q ^* is a limit in the limit value ^{_{(i * 2 1max -i d *}} 2) 1/2, if i _q ^** the limit If the value is exceeded, a limit value will be given. Due to the step change of the q-axis side current reference i _q ^* , the output PI _iq of the q-axis side PI control circuit 32q of the dq axis current control circuit 17 also increases. In this example, since the step amount of i _q ^** is large, PI _iq reaches the maximum value immediately. As a result, the q-axis side output signal v _q ^* of the d-q axis current control circuit 17 also increases by the increase in PI _iq , but even if a command value exceeding the outputtable voltage of the inverter is given, that much is actually. No voltage can be output. Therefore, the q-axis current i _q increases slowly.

Conventionally, the rate of increase eventually decreased due to insufficient voltage, and eventually the rate of increase became zero, and PI _iq remained saturated and could not be controlled. In the present invention, the PI controller 54 performs voltage control on the q-axis side based on the second voltage command value v _q ^** . The second voltage command value v _q ^** is v _q ^**
= (| V ^* _IMAX | ^2- _vd ^{* 2} ) ^1/2 . That is, the second voltage command value v _q ^** is the q-axis side output signal v _q ^*.
Is less than this value, the control on the d-axis side cannot be prevented.

When the q-axis side output signal v _q ^* exceeds the second voltage command value v _q ^** due to the step change of the q-axis side current reference i _q ^* , the PI controller 54 causes the d-axis current reference i _d ^*. Is increased in the negative direction. Since the d-axis side output v _d ^* of the d-q-axis current control circuit 17 also increases to the negative side by the PI control of the d-axis side current, the d-axis voltage maximum value setting unit 52 causes v _{q to change.}
The second given by ^** = (| v ^* _IMAX | ^2- _vd ^{* 2} ) ^1/2
The voltage command value v _q ^{** of} is decreased, and the d-axis current reference i _d ^* is further increased in the negative direction. As a result, the d-axis side output v _d ^* of the d-q axis current control circuit 17 increases to the negative side, and the q-axis voltage maximum value setter 52 sets v _q ^** = (| v ^* _IMAX |
² −v _d ^{* 2} ) ^1/2 second voltage command value v _q ^**
Decreases, and the d-axis current reference i _d ^* further increases in the negative direction, forming a positive feedback loop. This positive feedback loop, d-q-axis q-axis side output signal of the current control circuit 17 v _q ^* Do becomes smaller than the second voltage command value v _q ^**, the second voltage command value v _q ^** Until becomes zero,
The second voltage command value v _q ^** continues to decrease. In the case of FIG. 2, the voltage command value v _q ^** has reached zero. As a result, the d-axis current reference _id ^* rapidly increases in the negative direction.

Even after the voltage command value v _q ^** becomes zero, d
The shaft current reference _id ^* continues to increase in the negative direction. On the other hand, q
Since the shaft side current reference i _q ^* is limited at the output ^{_{(i * 2 tmax -i d *}} 2) 1/2 for q-axis current maximum value setter 55, to the d-axis current reference i _d ^* in the negative direction It decreases with an increase. The q-axis current i _q can hardly be increased due to insufficient voltage, but the deviation decreases as the q-axis side current reference i _q ^* continues to decrease, and the q-axis side current reference i _q ^* becomes the q-axis side. At time t ₂ when the current i _q is reduced to almost the same level, the dq axis current control circuit 1 is reached.
The output PI _iq of the q-axis side PI control circuit 32q of 7 is released from saturation and begins to decrease rapidly. As a result, the q-axis side output signal v _q ^* of the d-q axis current control circuit 17 also becomes small,
The output voltage command value of the inverter returns to a controllable range as a vector. Thus, now the current control of the d-axis side to operate effectively, the values of d-axis current i _d is likely to follow the d-axis current reference i _d ^*.

[0033] At time t _3, the d-axis current i _d is a value sufficiently close to the d-axis current reference i _d ^*, d-q-axis current control circuit 1
The d-axis side output v _d ^{* of 7} is sufficiently reduced. As a result, the second voltage command value v _q ^** , which has been zero, begins to increase. When the second voltage command value v _q ^** becomes equal to the q-axis side output signal v _q ^* of the dq axis current control circuit 17, the d-axis current reference id _d ^* stops increasing in the negative direction so far. Then
The d-axis current i _d is controlled to that value. Further, q-axis current command i _q ^* based on the d-axis current reference i _d ^* of the value at that time becomes a limit value by ^{_{(i * 2 tmax -i d *}} 2) 1/2, q -axis current i _q is controlled equal to its value. Accordingly, the d-axis side output v _d ^* of the d-q axis current control circuit 17,
Both the q-axis side output signal v _q ^* decreases to the value in the steady state. Finally, (v _q ^{* 2} + v _d ^{* 2} ) ^1/2 = | v ^*
_DMAX side output signal v _d ^* , which is _IMAX |, q axis side output signal v
The second voltage command value v _q ^** with a value that outputs _q ^* ,
The d-axis current reference i _d ^* and the q-axis current reference i _q ^* are stable.

[0034] Now, the control of the above, the current i _d of the permanent magnet motor is in a steady state, for i _q, d-
The vector sum (v _q ^{* 2} + v _d ^{* 2} ) ^1/2 of the d-axis side output v _d ^* and the q-axis side output v _q ^* of the q-axis current control circuit 17 is the output of the voltage vector length maximum value setting unit 51 | It is controlled to a value equal to v ^* _IMAX |. This means that the minimum d-axis current i _d for keeping the inverter output voltage at | v ^* _IMAX | is passed, and the q-axis current i _q is passed as much as possible.

In this way, the inverter output voltage is changed to | v ^*
Let us consider the operation when the minimum d-axis current i _d for keeping _IMAX | is flowed and the q-axis current i _q is flowed as much as possible and the rotation speed is increased. Since the speed electromotive force increases as the rotation speed increases, the q-axis side output v _q ^{* of the} control circuit 17 also increases. As a result, the second voltage command value v _q ^** is found in the same manner as described above, but the vector sum of the d-axis current i _d and the q-axis current i _q has already reached the inverter maximum current i ^* _tmax . Therefore, the second voltage command value v _q
By the q-axis voltage control by ^** , when the d-axis current reference _id ^* increases in the negative direction, the q-axis current command _iq ^* is immediately narrowed down. If the change in the number of revolutions is slow, the q-axis current command i _q ^* is narrowed down, and the q-axis side output v _q ^* of the control circuit 17 is lowered. Therefore, v _q ^* is the second voltage command value v _q ^{*. *} Can be followed, and the d-axis current i _d is gradually increased in the negative direction and the magnitude i _q of the q-axis current is controlled to decrease as the rotation speed increases.

The control circuit 17 reduces the second voltage command value v _q ^** due to a rapid change in the rotation speed and a rapid increase in speed electromotive force.
If the q-axis side output v _q ^* cannot follow, then the second voltage command value v _q ^** decreases, the d-axis current reference _id ^* increases in the negative direction, and the d-axis side output v _d thereby increases. Positive feedback similar to that at the time of the abrupt change of the torque current command described at the beginning, that is, increase of ^{* and} further decrease of the second voltage command value v _q ^** occurs. As a result, the d-axis current reference i _d ^* is transiently sufficiently increased, and the q-axis current command i _q ^* is sufficiently narrowed.
Not become uncontrollable, the inverter output voltage in the steady state after speed change | v ^* _IMAX | minimum d-axis current i _d to keep the shed, the q-axis current i _q as possible Shed

If the q-axis side output v _q ^* of the control circuit 17 does not exceed the second voltage command value v _q ^** in the torque constant region where the rotation speed is sufficiently low and the speed electromotive force is small, The control does not operate, the d-axis current reference i _d ^* remains zero, and the control is performed only on the d-axis side. That is, the operation is the same as that of the conventional control device in the constant torque region.

The multipliers 18d and 18q keep the current control loop gain constant when the DC voltage changes, and d
The d-axis side of the -q-axis current control circuit 17 outputs v _d ^*, q-axis side output v _q ^* when actually being output the d-axis voltage v _d, between the q-axis voltage v _q, d-axis side Output v _d ^* , q-axis side output v _q
There are two effects that the value becomes proportional as long as the value of ^* does not exceed the amplitude of the triangular wave of the PWM control circuit. The present invention positively utilizes the fact that the voltage commands v _d ^* , v _q ^* and the actually output voltages v _d , v _q have a proportional relationship.

That is, the output | v ^* _{IM AX} | of the voltage vector length maximum value setting unit 51 is controlled based on the voltage detection, and the voltage commands v _d ^* and v _q ^* are controlled as much as possible. Although not shown in the conventional example, the control so that the voltage commands v _d ^* and v _q ^* do not exceed | v ^* _IMAX | has already been actually performed. However, conventionally, the value of | v ^* _IMAX | had to be determined with a considerable voltage margin in order to ensure control stability. On the other hand, according to the present invention, | v ^* _IMAX | may be set to a value slightly lower than the maximum voltage that can be output by the inverter in the steady state, and a higher set voltage than the conventional one is possible. That is, the voltage utilization rate can be improved. However, if these are not desired, the voltage detection circuit 14
Also, the multipliers 18d and 18q can be omitted. In this case, the voltage vector length maximum value setter 51 sets the value that can be output even when the inverter DC voltage is the lowest | v ^*.
Must be set as _IMAX |. Also in this case, according to the present invention, the value of | v ^* _IMAX | can be made higher than that of the conventional system having no voltage detection circuit 14.

As described above, according to the present embodiment, it becomes unnecessary for the controller of the permanent magnet motor to flow the d-axis current i _d more than necessary to secure the stability of control. Moreover, the d-axis current i _d is automatically and rapidly increased when the torque current command suddenly changes or the rotational speed changes, and the q-axis current i _q is gradually increased while limiting the rate of change to a controllable range. It approaches the torque current command i _q ^** . If the q-axis current i _q matching the torque current command i _q ^** can be made to flow, of course, control is made so that that much current is made to flow. Minimum d to keep voltage at | v ^* _IMAX |
The axial current i _d and the q-axis current i _q as much as possible are automatically supplied. Therefore, the torque characteristic of the permanent magnet motor can be brought close to the theoretical value shown by the dotted line in FIG. That is, the output capacity of the permanent magnet motor can be increased, the operating frequency range can be expanded, and the efficiency can be increased, and the converter can be downsized when the output capacity of the motor is the same.

By the way, although the case where the converter is an inverter has been described so far, the present invention is also effective for a cycloconverter. In this case, a phase control circuit is used instead of the PWM control circuit. The voltage signal input to the voltage vector length maximum value setting unit 51 has the magnitude of the input side AC voltage because there is no DC voltage. Further, in the cycloconverter, the outputtable voltage decreases as the frequency increases, so that the voltage vector length maximum value setting device 51 functions not only as a voltage but also as a frequency. Other functions and effects are similar to those of the above-described first embodiment except that the voltage that can be output changes depending on the frequency. That is, the present invention can be applied to any system in which the voltage-type converter controls the dq axis current.

Further, when the electric motor is a synchronous electric motor, FIG.
The same circuit configuration can be used. However, the dq axis current control circuit 17 reflects the voltage-current equation of the synchronous motor. However, since the operation when the dq axis current control circuit 17 is viewed as a black box is the same as that of the permanent magnet electric motor, its contents are omitted.
The synchronous motor is different in that field control is performed, but the control in the constant field range operates in the same manner as in the permanent magnet motor. In the synchronous motor, the field is weakened in the high speed region so that the d-axis current does not have to flow from the armature side constantly even in the high speed region. However, since there is a time delay in the response of the magnetic flux to the field control, it was necessary to take a margin of the voltage into consideration, taking into consideration the transient phenomenon when the rotational speed increases. When the present invention is applied to the synchronous motor, the time delay of the response of the magnetic flux can be compensated by the d-axis current supplied from the armature side, and the control stability can be ensured. When the present invention is applied to the synchronous motor, the speed electromotive force becomes small if the magnetic flux is sufficiently weakened even in the high speed region. Therefore, compared to the second voltage command value v _q ^** , the dq axis current control circuit 17 d
The shaft-side output v _d ^* has a considerably small value, and the d-axis current i _d is controlled to zero in the steady state even in the high speed region, which is a difference from the case of the permanent magnet motor. When the magnetic flux weakening due to the field control is insufficient during the transition, the negative d-axis current i _d is caused to flow, while the q-axis current i _q is limited to stabilize the control, as described in the first embodiment. Secure the sex. As a result, the next weakening control start point can be set to a higher rotation speed than before. That is, the same effect as in the case of the permanent magnet motor can be obtained.

FIG. 3 shows an embodiment in which the present invention is applied to an induction machine drive system. In FIG. 3, 60 is an induction motor. The constant setter 55 used for setting i _d ^* in the range of zero or a negative value in FIG. 1 is omitted. That is, i _d ^* can take a positive value.
Reference numeral 61 is a constant setter that indicates the magnitude of the magnetic flux in the constant torque region, and 62 is a multiplier that outputs the result of multiplying the output of the constant setter 61 and the rotation speed signal ω _r output by the rotation detector 11. . A limiter 63 limits the output of the multiplier 62 by the output of the d-axis voltage maximum value setting device 52.
The output of the limiter 63 is given to the subtractor 53 as the second q-axis voltage command v _q ^** . dq axis current control circuit 1
Reference numeral 7 reflects the voltage-current equation of the induction motor.

With the above configuration, the output of the multiplier 62 is given as the second voltage command value v _q ^** at low speed.
Therefore, the q-axis voltage command value v _q ^* is controlled in proportion to the rotation speed ω _r . As a result, unlike the case of the first embodiment, the PI controller 54 operates even in the constant torque region, and the d-axis voltage command value i _d ^* that makes the magnetic flux constant is given to the d-q-axis current control circuit 17. To be When the rotation speed becomes higher and the output of the multiplier 62 becomes larger than the output of the q-axis voltage maximum value setting unit 52, the output of the q-axis voltage maximum value setting unit 52 is given as the second voltage command value v _q ^**. Therefore, as in the first embodiment, in the steady state, the inverter output voltage is controlled to the minimum d-axis current _id and the q-axis current i _q for maintaining | v ^* _IMAX |. When the voltage becomes insufficient during the transition, the d-axis current i _d is weakened, while the q-axis current i _q is limited, and the control is automatically controlled so as to ensure the control stability. As a result, the same effect as in the case of the permanent magnet motor can be obtained.

[0045]

As described above, according to the present invention,
In the steady state of the control device for the AC motor, the minimum required d-axis current i _d is flowed, so that the torque component current that can be generated in the constant output region can be increased as compared with the related art. Further, when the operating state changes, the d-axis current i _d is automatically and rapidly increased to limit the q-axis current i _q to a controllable range.
Achieve stable control. This makes it possible to bring the torque characteristics of the AC motor closer to the theoretical value in the steady state.

As described above, it is possible to increase the output capacity of the AC motor, expand the operating frequency range, improve efficiency, and downsize the converter.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a waveform chart for explaining the operation of FIG.

FIG. 3 is a configuration diagram of another embodiment of the present invention.

FIG. 4 is a configuration diagram of a conventional example.

5 is a vector diagram for explaining the operation of FIG.

FIG. 6 is a vector diagram for explaining the operation of FIG.

7 is a block diagram showing a configuration of a dq axis current control circuit in FIG.

FIG. 8 is a vector diagram for explaining the operation of FIG.

FIG. 9 is a characteristic diagram of a conventional example.

[Explanation of Codes] 3 Inverter 4 Permanent magnet motor (AC motor) 11 Rotation detector 12 Current detector 13 UVW / dq coordinate conversion circuit 14 Voltage detector 17 dq axis current control circuit 19 dq / UVW Coordinate conversion circuit 51 Voltage vector length maximum value setter 52 q-axis voltage maximum value setter 54 PI controller 55 Constant setter 56 q-axis voltage maximum value setter 57 Limiter

Claims (4)

[Claims] 1. A current flowing from an electric power converter to an AC electric motor is based on a magnetic flux direction of the AC electric motor on dq axis coordinates composed of a d axis parallel to the magnetic flux direction and a q axis perpendicular to the magnetic flux direction. The q-axis voltage command value v _q ^* is controlled so that the q-axis current i _q follows the q-axis current command value i _q ^* created based on the torque current command given as the components i _d and i _q. , The d-axis voltage command value v _d ^* is controlled so that the d-axis current i _d follows the d-axis current command value i _d ^* created based on the output voltage of the power converter, and the q-axis voltage In an AC motor controller that controls the output voltage of the power converter based on the command value v _q ^* and the d-axis voltage command value v _d ^* , a predetermined value | v related to the outputtable voltage of the power converter
_{Based on IMAX} |, the d-axis voltage command value v _d ^*, and the q-axis voltage command value v _q ^* , the d-axis current command value i _d ^* is controlled to obtain a current that can be output by the power converter. The q-axis current command value i _q is limited by limiting the torque current command based on the related predetermined value | i _IMAX | and the d-axis current command value i _d <sup>*.
* The</sup> AC motor control device characterized by the following. 2. The AC motor control device according to claim 1, wherein a predetermined value | v related to the outputtable voltage of the power converter.
_{From IMAX} | and the d-axis voltage command value v _d ^* , v _q ^** = (|
v _IMAX | ² −v _d ^{* 2} ) ^1/2 and the second q-axis voltage command value v _q
^** , and the d-axis current command value i based on the comparison between the second q-axis voltage command value v _q ^** and the q-axis voltage command value v _q ^*.
The magnitude of _d ^* is controlled, and a value (| v _IMAX | based on a predetermined value | i _IMAX | related to the current that can be output by the power converter and the d-axis current command value i _d ^{* 2-} i
_The AC motor control device is characterized in that the magnitude of the torque current command is limited by _d ^{* 2} ) ^1/2 to obtain the q-axis voltage command value i _q ^* . 3. The AC motor control device according to claim 1, wherein a voltage source PWM inverter is used as the power converter,
Based on the detection of the DC voltage of the inverter, the q-axis voltage command value v _q ^* and the d-axis voltage command value v _d ^*, and the q-axis voltage v _q and the d-axis voltage v _d actually output from the inverter.
In order to maintain the proportional relationship with
A predetermined value | v _IMAX | that corrects the relationship between the axial voltage command value v _q ^* and the d-axis voltage command value v _d ^{* and} is related to the outputtable voltage of the power converter based on the detection of the DC part voltage.
A control device for an AC electric motor, characterized in that 4. The AC motor control device according to claim 2, wherein the AC motor is an induction motor, and the predetermined value | v related to the outputtable voltage of the power converter.
_The q-axis voltage limit value (| v _IMAX | ² −v _d ^{* 2} ) ^1/2 is obtained from _IMAX | and the d-axis voltage command value v _d ^*, and the q-axis is given in proportion to the rotation speed of the induction motor. The voltage command value is limited by the q-axis voltage limit value (| v _IMAX | ² −v _d ^{* 2} ) ^1/2 to obtain the second q-axis voltage command value v _q ^** ,
The magnitude of the d-axis current command value i _d ^* is controlled based on the comparison between the second q-axis voltage command value v _q ^** and the q-axis voltage command value v _q ^*, and the power converter i _IMAX | | and the d-axis current command value i _d ^* and the value based on ^{_{(| i IMAX | 2 -i d}} * 2) the magnitude of the torque current command by ^1/2 a predetermined value associated with the output current that can be Is set to the q-axis voltage command value i _q ^* , and the AC motor control device is characterized in that: