JP3106471B2 - Vector control method of induction motor - Google Patents

Description

Description of the Related Art [0001] The present invention relates to a vector control method for an induction motor driven by a current type (vector control type) inverter.

[Conventional technology]

FIG. 1 is a control command system diagram when an induction motor is driven by a conventional control method.

When the speed command Nref of the induction motor 6 is given to the calculator 8, the calculator 8 calculates the speed deviation between the speed command Nref and the feedback speed N from the speed detector 7 connected to the rotation shaft of the induction motor 6. Output to speed controller 1. The speed controller 1 outputs a secondary current command value I2 * of the induction motor 6 to the vector controller 2 based on the input of the speed deviation. Return speed N
Is also input to the magnetic flux commander 3, and the magnetic flux commander 3
The command secondary magnetic flux amount Φ * of the induction motor 6 in a pattern corresponding to the feedback speed N is output to the vector controller 2.

The vector controller 2 performs a vector operation based on the input of the secondary current command value I2 * and the command secondary magnetic flux amount Φ *, and converts the command primary current i1 * of the induction motor 6 into a current type (vector control type) inverter 4. Output to Thereby, the primary current i1 from the AC power supply 5 to the induction motor 6 is controlled,
The induction motor 6 is driven while maintaining a constant torque or a constant output at the command speed Nref.

By the way, generally, the output P of the induction motor is expressed by the following equation (1).

 P = K1, N, I2, Φ (1) where K1 is a constant, N is the rotation speed of the induction motor, I2 is the secondary current value of the induction motor, and Φ is the amount of secondary magnetic flux of the induction motor.

Here, when N> Nb, Φ = (Nb / N) · Φ0 (2) However, Nb is the base speed of the induction motor (fixed), N is the speed of the induction motor, and Φ0 is the rating of the induction motor. Assuming the amount of secondary magnetic flux, from equation (1), P = K1 · Nb · I2 · Φ0 (3), and if the secondary current value I2 of the same induction motor, the output P of the induction motor is constant. Becomes

FIG. 4 is a characteristic diagram of the rotation speed and the command secondary magnetic flux amount (magnitude of the command magnetic flux) Φ ^* in the magnetic flux commander at this time.

When the induction motor 6 rotates forward, the rotation speed N is increased from the start [rotation speed 0] while maintaining the rated secondary magnetic flux amount Φ0 of the induction motor, and the basis of the calculation for converting from constant torque control to constant output control is maintained. When the rotation speed reaches the base rotation speed Nb (which shifts along the straight line 21), the motor is driven in the constant output region up to the maximum rotation speed NMax according to the quadratic curve 43.

In this case, the condition Φ = (Nb / N) · Φ0 in the equation (2) is satisfied.
At the maximum rotation speed NMax, Φ = (Nb / NMax) · Φ0.

The characteristic curves 22 and 44 going leftward from the rotation speed N = 0 are the same in the case of reverse rotation.

FIGS. 5 (a) and 5 (b) show characteristic diagrams of the time change for each of the rotational speed N of the induction motor and the time derivative of the secondary magnetic flux amount Φ in this case.

That is, the change of the rotation speed N of the induction motor 6 over time t becomes a curve 5a, and at time t1, it becomes the base rotation speed Nb.
At t2, the rotation speed reaches the maximum rotation speed NMax.

The temporal change in the time derivative of the secondary magnetic flux amount Φ in this driving operation is 5b, and the change from the time point t1 to the time point t2 is remarkable.

[Problems to be Solved by the Invention] However, in the conventional control method, when the induction motor 6 is accelerated in a short time, the constant output from the constant torque region is caused by the change of the characteristic curve 5b in FIG. 5 (b). When entering the area (t
In 1), the voltage and current of the induction motor 6 oscillate, and as a result,
There is also a problem that vibration occurs in the rotation speed N.

Accordingly, the present invention provides a method for performing constant output control in which voltage and current oscillations are less likely to occur even during rapid acceleration / deceleration.
With that purpose.

[Means for solving the problem]

In order to achieve the above object, the present invention controls the secondary current of the induction motor based on the deviation between the detected rotation speed of the induction motor and the speed command, and controls the secondary current of the induction motor based on the input of the detected rotation speed. When controlling the amount of secondary magnetic flux and further controlling the primary current based on the secondary current and the amount of secondary magnetic flux, the control region for the amount of secondary magnetic flux is divided into a constant torque region and a constant output region, In the torque region, the magnetic flux constant control is performed so that the amount of the secondary magnetic flux is constant regardless of the change in the detected rotational speed. In the constant output region, the amount of the secondary magnetic flux decreases as the detected rotational speed increases. In the vector control method of the induction motor for performing the magnetic flux weakening control as described above, the decrease of the secondary magnetic flux amount is made linear, and the constant value is set so that the time differential value of the secondary magnetic flux amount becomes constant. Performing flux-weakening control in the region, characterized in that.

[Action]

According to the present invention, since the magnetic flux weakening control in the constant output control is performed so that the rate of change of the magnetic flux is constant, it is possible to minimize the occurrence of voltage and current vibrations during acceleration / deceleration of the induction motor. .

〔Example〕

FIG. 2 shows a characteristic curve diagram of the command secondary magnetic flux amount (magnitude of the command magnetic flux) Φ ^* with respect to the rotation speed N in one embodiment of the present invention.

3 (a) and 3 (b) show characteristic curves for the time t of the rotational speed N of the induction motor and the time derivative of the secondary magnetic flux amount Φ in that case.

 In all the drawings, the same reference numerals denote the same elements.

By the way, the vector expression φ of the amount of secondary magnetic flux of the induction motor 6 is expressed by the following equation.

φ = Φε ^jωt (4) where ε ^jωt is the angular velocity ωt [ω = 2πf f is the frequency t
Is a unit vector that rotates at time].

The voltage e induced by the amount of secondary magnetic flux φ of the induction motor 6
Will be ^{e = dφ / dt = jωΦε jωt} + (dφ / dt) ε jωt ...... (5). Further, the induced voltage e acts as one of disturbances in the current control.

Here, the constant output pattern shown in FIG.
When the induction motor 6 is accelerated from the stop state [N = 0] to the maximum rotation speed NMax in the constant torque region, the curve 43 is obtained from the curve 43 from the curve 21 and the curve 44 from the straight line 22 in the reverse rotation.
Since φ / dt = 0, the second term on the right side of the equation (5) is zero, but the change is the largest at the time when the constant output area is entered. The change of the second term on the right side of equation (5) during acceleration is shown in FIG. 5 (b) [curve 5b].

Therefore, the present invention accurately captures such a phenomenon and obtains a characteristic curve of the command secondary magnetic flux amount (magnitude of the command magnetic flux) Φ ^* of the magnetic flux commander 3 in the circuit configuration diagram of FIG. The figure is set as shown in FIG.

The curve 43 in the constant output region as seen in the conventional example is adjusted to the straight line 23 to control the magnitude Φ ^* of the command magnetic flux of the magnetic flux commander 3 to the vector controller 2.

In this manner, the rotation speed N pattern of the magnitude Φ ^* of the command magnetic flux in the constant output region is adjusted.

Therefore, the induction motor 6 is stopped (N =
0] to the maximum rotation speed NMax, the flux change rate is zero (dφ / d) in the constant torque region as in the conventional case.
(t = 0), the second term on the right side of the equation (5) becomes zero. Then, when entering the constant output region at time t1, the magnetic flux change rate is not zero, but its value becomes constant as shown by the straight line 3b in FIG. 3 (b). Even if the current changes, the occurrence of the vibration can be avoided. Further, by making the magnetic flux change rate constant, the value of the magnetic flux change rate at time t1 itself can be made smaller than in the conventional art, as is clear from FIG. 3 (b). The transition of the control to and from the area can be performed more smoothly.

〔The invention's effect〕

Thus, according to the present invention, when performing constant output control in the vector drive of an induction motor, generally, a magnetic flux Φ (excitation current) command is inversely proportional to the rotation speed N of the induction motor (Φ∝1 / N) in a constant output range. ) Function,
Recently, the demand for acceleration and deceleration in a short time has caused a phenomenon in which the rotational speed at the point when the motor enters the constant output region from the constant torque region appears, which has been a major issue in this technical field. Wiping and a remarkable effect can be exerted on smooth operation of constant output control.

[Brief description of the drawings]

FIG. 1 is a control command system diagram when an induction motor is driven by the control method of the present invention, and FIG. 2 is a rotation of a command secondary magnetic flux amount (magnitude of a command magnetic flux) Φ ^* in one embodiment of the present invention. FIG. 3 (a) and FIG. 3 (b) are characteristic curve diagrams for the speed N and the time derivative of the rotational speed N of the induction motor and the time derivative of the secondary magnetic flux amount Φ, respectively. FIG. 4, FIG. 5 (a) and FIG. 5 (b) are explanatory views of the conventional example. DESCRIPTION OF SYMBOLS 1 ... Speed controller 2 ... Vector controller 3 ... Magnetic flux commander 4 ... Current source inverter 5 ... AC power supply 6 ... Induction motor 7 ... Speed detector 8 ... Calculator N ... Induction motor Rotational speed (return speed) Nb: Induction motor base speed NMax: Induction motor maximum speed.

Claims (1)

(57) [Claims] A secondary current of the induction motor is controlled based on a deviation between a detected rotation speed of the induction motor and a speed command, and a secondary magnetic flux amount of the induction motor is controlled based on an input of the detected rotation speed. Further, when controlling the primary current based on the secondary current and the secondary magnetic flux amount, the control region for the secondary magnetic flux amount is divided into a constant torque region and a constant output region,
In the constant torque region, the magnetic flux constant control is performed so that the amount of the secondary magnetic flux is constant irrespective of the change in the detected rotational speed. In the constant output region, the amount of the secondary magnetic flux decreases as the detected rotational speed increases. In the vector control method of the induction motor that performs the magnetic flux weakening control such that the decrease of the secondary magnetic flux amount becomes linear,
A vector control method for an induction motor, comprising: performing a magnetic flux weakening control in the constant output region so that a time differential value of the secondary magnetic flux amount becomes constant.