JPS63314193A - Method of controlling flux of motor - Google Patents

Abstract

PURPOSE:To reduce noise generated by an induction motor, by controlling flux in accordance with the speed of the motor, in the case of driving an elevator having a given speed-torque pattern. CONSTITUTION:When starting command has arrived, a speed pattern generator 11 generates speed commanding values V' sequentially as determined previously. A flux operator 12 compares the speed commanding value V', obtained from the speed pattern generator 11, with a branch point speed upon operating flux to operate a flux commanding value phi and output it to a vector control unit 14. A speed difference operator 13 receives the speed commanding value V' from the speed pattern generator 11 and a detecting moving speed V from an actual speed operator 9 and operates a torque commanding value (r) to output it to the vector control unit 14. The vector control unit operates an instantaneous flux and a time torque to output a signal, putting an inverter ON/OFF, to an inverter unit 4.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention operates an induction motor driven by a variable voltage, variable frequency inverter, and operates the motor at a fixed speed and torque pattern from start to stop, like an elevator. The present invention relates to a control method for operating a device with low noise.

[Conventional technology]

In place of DC machines, which were conventionally widely used when controllability was required, in recent years induction machines, which are inexpensive and easy to maintain, have been driven by slip frequency control, constant V/f control, vector control, etc. It is now possible to drive with the same performance.

These induction motor controls operate the induction motor by converting the input three-phase AC power into smoothed DC power at the converter section, and then converting the DC power into AC at the desired frequency at the inverter section. be.

The above-mentioned inverter section is composed of semiconductor elements such as transistors and self-extinguishing thyristors (GTOs), and these semiconductor elements are turned on and off to obtain alternating current, but generally a pulse width control method is used. Therefore, the AC current i (t) obtained here includes harmonics expressed by the following equation in addition to the desired frequency.

1(t) J ancosn#t+'f' bnsinn
a+t ・−・−・−・・・−■rF”I
n''1, # is the angular frequency, and T is the time of one period of i (t).

By the way, V/f constant control and slip frequency control control the torque by keeping the magnetic flux constant, and the generated torque f is expressed as the magnetic flux φt=kr・φ・manufacturing as shown in the following equation.
・・Dan・・Dan・・・Seal・・Dan・
(2) Here, Vd& is the DC side voltage of the inverter, and kφ and Ni are constants related to magnetic flux and torque, respectively.

An example of constant V/f control using a conventional pulse width control (PWM) inverter will be described below with reference to the drawings.

FIG. 6 is a block diagram of an example of a V/f constant control PWM inverter. The converter section 2 receives AC power from a three-phase AC power supply 1, converts it into DC, and smoothes the DC voltage by a smoothing section 3 consisting of a capacitor etc. It is supplied to the inverter section 4 as DC power of Vdc.

The inverter section 4 turns on the built-in semiconductor elements in response to on/off signals from the inverter control section 8.

It is turned off and AC power is supplied to the induction motor 5 to drive it.

The inverter control unit 8 receives the speed command from the speed command unit 6, adjusts the pulse width of the carrier wave having a predetermined frequency, and adjusts the three-phase AC output of the inverter unit 4 to a frequency corresponding to the commanded speed and that frequency. Generates on and off signals so that the voltage is proportional.

Although not shown in FIG. 6, the induction motor 5 may be used as needed.
The speed of the inverter is detected, a feedback signal is sent to the inverter control unit 8, and the frequency and the voltage proportional to the frequency are finely adjusted by well-known means, thereby improving and stabilizing the speed accuracy.

[Problem that the invention seeks to solve]

In pulse width control type variable voltage, variable frequency inverters, the carrier frequency is often about 1 to 3 kHz, and when the harmonic components become large, a particularly harsh sound becomes louder, causing discomfort to people. give.

Therefore, if such induction motor control is used as it is, for example, as an elevator driving device, it is generally inconvenient that passengers in the car located directly below the induction motor will feel uncomfortable.

In order to reduce the so-called magnetic noise that causes discomfort, it is necessary to reduce the magnetic flux φ obtained by the equation 0, but since the generated torque t is proportional to the magnetic flux φ as shown in the equation 0,
Simply reducing the magnetic flux φ does not generate enough torque to meet the total required torque of the load torque and acceleration torque during acceleration, which poses a serious problem for elevators.

For example, in induction motor control used in places where there are rapid load fluctuations, such as steel lines, it is necessary to always maintain a rated torque or, depending on demand, a torque greater than the rated torque. Conversely, in equipment that operates at a constant speed and torque pattern, such as an elevator, the torque required during acceleration and deceleration is large, but the torque required during constant running is small, and at this time the magnetic flux There is no problem even if the amount is reduced, but in the past, the voltage was controlled in proportion to the frequency so that the amount of magnetic flux could generate the required torque during acceleration and deceleration. That is, during constant speed operation, overexcitation occurs, which often causes unpleasant magnetic noise.

[Means for solving problems]

The magnetic flux control method for an electric motor according to the present invention employs a control device that can arbitrarily change the torque by controlling the magnetic flux command value, and when the torque required from the load side is uniquely determined by the speed of the electric motor. The present invention is characterized in that the relationship between speed and torque is memorized and the minimum magnetic flux command value that can produce the required torque according to the operating speed of the electric motor is determined.

[For production]

Although the magnetic flux control method for an electric motor according to the present invention is applied only when the torque required from the load side is uniquely determined by the speed of the electric motor, it is possible to always operate with the minimum necessary magnetic flux at each speed. Therefore, there is less opportunity for the harmonic magnetic flux that generates harsh noise to increase, making it possible to operate with low noise.

〔Example〕

A case will be described in which the magnetic flux control method for an electric motor according to the present invention is applied to driving an elevator. Figure 2 is a diagram showing the speed and torque patterns in elevator operation, where the horizontal axis is all time, (al is the speed pattern, (b)
represents the acceleration at each time, and (C) represents the required torque pattern at each time.

At time to, which is the start-up time, the engine is started with a small acceleration so as not to cause any shock to the passengers, and after the start-up, the acceleration is linearly increased until the speed reaches v2 at time 11. The acceleration is kept constant until the speed reaches vl from v2, and after the speed reaches vl at time t2, the acceleration decreases linearly, and at time t3 the acceleration becomes O.
After the speed reaches v4, the vehicle partially operates at speed v4.

The procedure for stopping and starting is the reverse, and the time t
At time t5, the deceleration starts, but in order to gradually decelerate so as not to give the passengers any shock, the deceleration is increased linearly until the speed reaches vl at time t5.The speed changes from vl to v2. The deceleration is kept constant until the speed reaches V! at time t6. After reaching this point, the deceleration is decreased linearly, and at time t7, the deceleration reaches O and the speed also becomes 0, and the motor stops. Here, it is assumed that the absolute values of the maximum acceleration and the maximum deceleration are equal, and that their rates of change are also equal in absolute value only with different signs.

The torque t required at each time under such operating conditions is as shown in FIG. 2(C). In FIG. 2(e), the solid line on the positive side indicates the torque required when the elevator is running up, and the dashed line on the negative side indicates the torque required when the elevator is running down.

The torque required to support the elevator's own weight is fL
and the maximum acceleration between time t1 and t2 or time 1s-
Assuming that the torque required to accelerate or decelerate the dead weight at the maximum deceleration between ta is TL, the torque required to operate the elevator is as follows.

First, when the elevator is in ascending operation, the required torque is TL at the time of startup, that is, when the speed is O, and since the acceleration increases linearly until the speed reaches vl when the time is ri, the required torque is also changed from TL to (rL + t m). ) increases linearly up to Time t1~t! Since the acceleration is constant at the maximum acceleration during the period, the required torque from v2 to Vsj is constant (rl,-)-tm). Time 1
．． ~ t3, the acceleration decreases linearly, so the velocity becomes v
The required torque to increase from l to v4 is (tl, +
decreases linearly from vm) to vL.

During the time ts''wta, the speed remains constant at v4 and there is no acceleration or deceleration, so the required torque also remains constant at TL.

Since deceleration starts at time t4 and increases linearly until the speed drops to vl at time tl, the required torque changes linearly from 1L to (rz-mum) at time 01. -16, the maximum deceleration remains constant and the required torque remains constant until the speed decreases from vs to v2.

Since the deceleration decreases linearly between times t and t1, the required torque for the speed to reach a stop from v8 is (TL
-Ym) to rL.

Using the same concept when the elevator is moving downward, the required torque from stop to speed v2 is from -tL to -(TL
-TL), the required torque during speed increase from speed v2 to vs is constant at -(1L-fL), speed v3
The required torque during speed increase from -(Q, -t) to v4 changes linearly from -(Q, -t) to -fp. When the speed is constant v4, the required torque during operation is constant 1L, and when the speed changes from v4 to v
The required torque during deceleration to s is from -tL to -('L+tm)
The required torque while decelerating from Vl to V2 is constant at -(tL+rm), and the required torque while decelerating from V2 to stop is -(r)-1-rm)
It changes linearly from -fL◎ In other words, the absolute value of the required torque exceeds 1L only during acceleration from 0 to V4 when the elevator is running up, and when the elevator is running down the elevator Time is speed v4
Only during deceleration from to 0.

The gist of the present invention is to increase the magnetic flux of the induction motor only when a particularly large torque is required, and in the case of elevator operation mentioned above, the relationship between speed and required magnetic flux is as shown in the graph in Figure 3. It becomes like this.

What torque is required for constant speed operation? Four magnetic fluxes are required to generate L, and the maximum torque required at maximum acceleration/deceleration (rL+
Letting φM be the magnetic flux required to generate V.

When the speed is between 0 and v2, φ* = kv* + φd ・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・ ■Speed is v2 ~
Between v3 φ*2φM ・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・■Speed is V3-V
During 4, φ*=φy1-k (v*-v3)...
・・・・・・・・・・・・・・・・・・■Here I, k
is a constant determined by the normal magnetic flux φT, the maximum magnetic flux φM, and the speed v2, and φM−φT k = .

FIG. 1 is a block diagram of an embodiment in which the magnetic flux control method for an electric motor according to the present invention is applied to a conventional PWM inverter, and the same reference numerals as in FIG. 6 indicate parts that are the same or have the same functions. Conventional V/f constant control PWM shown in Fig. 6
The difference from the case using an inverter is that the magnetic flux calculation unit 7
has been added.

The speed command section 6 incorporates the speed pattern of the elevator shown in FIG. The magnetic flux calculation unit 7 calculates the magnetic flux command value φ8* from the speed command value V using one of formulas 0 to 0 only when a large torque is required during acceleration in elevator ascending operation or deceleration in descending operation. In other cases, the magnetic flux command value φ8 is the normal magnetic flux φ
Let it be T. The calculated magnetic flux command value φ3 and speed command value - are sent to the inverter control section 8'.

*The inverter control unit 8' controls the speed command value V and the magnetic flux command value φ8.
By adjusting the pulse width of the carrier wave having a predetermined frequency, the three-phase AC output of the inverter section 4 becomes a frequency corresponding to the speed command value V* and a voltage at which the motor magnetic flux at that frequency becomes φ. Thus, the inverter section 4 generates on/off signals.

By adopting such a magnetic flux control method for the electric motor, it is possible to operate the electric motor using a small magnetic flux (except when a particularly large magnetic flux is required), and low-noise operation can be performed.

In recent years, 10 of IEEJ Transactions B published in January 1986
As explained in the paper titled "New high-speed torque control method for induction motors based on instantaneous slip frequency control" published in Vol. -Convert to q2 axis to obtain instantaneous space vector.

An inverter control method has also been developed in which the instantaneous spatial magnetic flux vector is calculated directly from these voltages and currents to control the magnetic flux.

FIG. 4 shows a block diagram of an embodiment in which the motor magnetic flux control method according to the present invention is applied to this instantaneous space vector control. The same symbols as in Fig. 6 indicate parts that are the same or have the same functions.・Instantaneous space vector control has excellent controllability such as transient response, but the magnetic flux calculation accuracy at low speeds is slightly poor*. , the magnetic flux command value φ in the low speed range is set higher than the required magnetic flux.

* FIG. 5 is a graph showing the magnetic flux command value φ at each speed command value V in this embodiment. In the low speed range where magnetic flux calculation accuracy is poor, the magnetic flux command value φゝ is set to a special magnetic flux φL constant in the range from stop to the resistive speed vl, and from speed v1 to v2, the magnetic flux is decreased linearly to set the speed. V! The magnetic flux command value φ at the maximum magnetic flux φM
shall be. The speeds between v2 and v4 are the same as in the previous embodiment shown in FIG.

Expressing this as a formula, φ9=φL while the speed is Q-y* ・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・■Speed is V! ~v2 φ=φL −k' (v*−Vl)・・・・・・・・・
・・・・・・・・・・・・・・・・・・■ Tree here ′ is special magnetic flux φL, maximum magnetic flux φM and speed v
1. A constant determined by V2.

The magnetic flux control method in this embodiment will be explained with reference to the block diagram shown in FIG. Reference numeral 10 denotes a start/stop signal generator, which instructs the speed pattern generator to start and end its operation. When the speed pattern generator 11 receives a start command, it sequentially generates speed command values V as predetermined. ,
It is sent to the magnetic flux calculator 12 and speed deviation calculator 13.

The magnetic flux calculator 12 calculates the speed command value V obtained from the speed pattern generator 11 and the branching point speed Ml + on the magnetic flux calculation of formulas 1 to 3.
V2 + vl is compared, and a magnetic flux command value φ is calculated using one of the arithmetic expressions. For example, if the speed command value V* is larger than the speed v1 (less than v2, the magnetic flux command value φ is calculated by the formula 0. The calculated magnetic flux command value φ is output to the vector control section 14. 15 is the induction motor 5. This is a rotational speed detector that detects the rotational speed, and sends the detected rotational speed to the actual speed calculator 9.The actual speed calculator 9 calculates the moving speed V of the elevator from the rotational speed of the induction motor, and converts it into a speed deviation calculator. Output to 13.

The speed deviation calculator 13 receives the speed command value V from the speed pattern generator 11 and the detected moving speed from the actual speed calculator 9, compares them, and calculates the required torque pattern force shown in FIG. 2 (Cl). 1, a torque command value *T is calculated and output to the vector control unit 14.

In the vector control section, based on the input voltage Vdc of the inverter 4 and the phase currents Iu, Iv, and Iw of the induction motor,
.

The instantaneous magnetic flux φ and the instantaneous torque t are calculated using the equation 0, and a signal is sent to the inverter unit 4 to turn on and off the conductive elements constituting the inverter so that these match the command values.

〔Effect of the invention〕

As described in detail above, in a case where the motor has a fixed speed-torque pattern, such as an elevator drive, the noise generated by the induction motor can be reduced by controlling the magnetic flux according to the speed. Furthermore, the excitation current among the induction motor currents is a current that does not directly contribute to the generation of torque, and reducing the magnetic flux when the generated torque may be small also leads to an improvement in the power factor.

In the above description, the case where an induction motor is driven by an inverter has been described, but it is obvious that the present invention can be applied to other types of motors 2 whose excitation current can be controlled, such as DC motors and their field control.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment in which the magnetic flux control method for an electric motor according to the present invention is applied to a conventional PWM inverter, and Fig. 2 is a diagram showing speed and torque patterns in elevator operation. (b) shows the acceleration at each time, (C) shows the required torque pattern at each time, FIG. 3 is a graph showing the required torque at each speed, and FIG. 4 shows the instantaneous space vector control according to the present invention. This is an example of a case where such a magnetic flux control method for an electric motor is applied. Figure 5 is a graph showing the magnetic flux command value for each speed command value in this example, and Figure 6 is a graph showing the V/f constant control PW.
It is a professional diagram of an example of an M inverter. l...3-phase AC power supply, 2...group converter section, 3...smoothing section, 4...inverter section, 5...induction motor, 6... Speed command unit, 7... Magnetic flux calculation unit, 8... Inverter control unit, 9... Actual speed calculation unit, 10...
... Start/stop signal generator, 11... Speed pattern generator, 12... Magnetic flux calculator, 13...
. . . Speed deviation calculator, 14 . . . Vector control unit, 15 . . . Rotation speed detector.

Claims (1)

[Claims] In a motor rotation speed control device that can arbitrarily change the torque by controlling the magnetic flux command value, when the torque required from the load side is uniquely determined by the speed of the motor, the relationship between the speed and torque is memorized. 1. A magnetic flux control method for an electric motor, comprising: determining a minimum magnetic flux command value that can produce a required torque according to the operating speed of the electric motor.