JPH07123764A - Induction motor control method and apparatus - Google Patents

Abstract

(57) [Summary] [Purpose] To always obtain a prescribed starting acceleration regardless of changes in the primary resistance and secondary resistance of the induction motor. The internal magnetic flux density B _s ′ of the induction motor 1 is detected by the Hall element 16, passes through the gain constant circuit 17 and the low pass filter 18, and is given to the adder 19 as the internal magnetic flux density B s. The adder 19 outputs the deviation ΔB between the magnetic flux density set value B _o from the setter 20 and this B _s . The gain constant circuit 21 outputs the slip frequency correction amount Δf _sB based on this deviation _ΔB . The adder 14 subtracts this Δf _sB from the slip frequency reference value f _so and outputs the slip frequency f _s . The adder 10, the inverter frequency f, the power running, and outputs it as _{f = f} r + _{f s,} during regenerative outputs as _{f = f} r -f _s.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method and control device for an induction motor used in, for example, an electric vehicle.

[0002]

2. Description of the Related Art Conventionally, for example, PWM control at the time of starting an induction motor driven by a variable voltage variable frequency inverter power source used in an electric vehicle is mainly divided into the following two modes.

One of them is a mode shown in FIG. 5, which is called an asynchronous mode for generating a variable voltage variable frequency in which the carrier frequency at an extremely low frequency including 0 Hz starting is constant.

In FIG. 5, the induction motor 1 is driven by the input of AC power of variable voltage and variable frequency from the PWM inverter 2. The speed of the induction motor 1 is detected by the speed detector 3, and the output current of the inverter 2 is detected by the current detector 4.

The setters 5, 6 and 7 output the modulation rate reference value γ _o , the current command value Is and the slip frequency reference value f _so for the inverter 2, respectively. Also,
9 and 10 are adders, 11 and 12 and 13 are gain constants K
It is a gain constant circuit that gives γ, KI, and Kr.

In this asynchronous mode, as shown in FIG. 7, a frequency range of about 0 to 10 Hz is usually used. Then, the slip frequency fs is fixed, and a predetermined starting current I is applied to the rotor frequency fr calculated from the output of the speed detector 2 for detecting the rotation speed of the induction motor 1.
The inverter 3 outputs the frequency f and the voltage V that are s.

That is, to briefly explain the operation of FIG. 5, the rotation speed of the induction motor 1 detected by the speed detector 3 is given by the gain constant circuit 13 as the rotor rotation speed fr. The adder 10 uses the rotor rotation frequency fr.
If, from the slip frequency reference value fso from the setting device 7, the power running time is f = f _r + f _so, during regeneration outputs the inverter frequency f given by f = f _r -f _so. The setter f outputs the modulation rate reference value γ _o based on the input of the inverter frequency f.

The output current Im 'of the inverter 2 given by the current detector 4 is given as the output current Im by the gain constant circuit 12. The adder 9 outputs the deviation ΔI between this output current Im and the current command value Is from the setter 6. The gain constant circuit 11 outputs the modulation rate correction amount Δγ based on this deviation ΔI. The adder 8 outputs to the inverter 2 a value γ obtained by correcting the modulation rate reference value γ _o from the setting device 5 based on the correction amount Δγ.

On the other hand, in the frequency region higher than the asynchronous mode, as shown in FIG. 7, the region up to the maximum frequency for PWM control is divided into several regions, and in the frequency region of one block, FIG. 6 called a synchronous mode in which the number of pulses in one cycle of the output waveform is fixed and the carrier frequency and the output frequency are changed at a constant ratio.
The mode shown in is used. In this synchronous mode, the output voltage V with respect to the output frequency f is fixed, and the slip frequency f
By changing _s , control is performed so that a predetermined starting current Is is obtained.

That is, in the asynchronous mode of FIG. 5, the modulation factor γ is set by the adder 8 and the gain constant circuit 11.
However, in the synchronous mode of FIG. 6, the slip frequency f is changed by the adder 14 and the gain constant circuit 15.
Is made variable. In the above description, the control block diagrams of the asynchronous mode and the synchronous mode are separately shown in the two drawings of FIGS. 5 and 6 for the sake of clarity, but in reality, the illustration is omitted. By a certain switching means, the state of FIG. 5 is switched to the state of FIG.

By the way, the reason why the control is performed separately in the two modes as described above is as follows. First, the torque of the induction motor 1 is calculated from the equivalent circuit of FIG.

[0012]

[Equation 1] It is represented by. Here, r ₁ is a primary resistance, r ₂ ′ is a secondary resistance, x ₁ is a primary inductance, x ′ ₂ is a secondary inductance, P is the number of poles, and s is a slip.

Then, the area of large f, and thus small s, such as the synchronization mode, is expressed by the following equation (1):

[0014]

[Equation 2] Therefore, when trying to obtain a constant torque at the time of starting, V1 / f is made constant in the equation (3), and f · s,
That is, the slip frequency f _s should be constant.

However, if the temperature changes depending on the use conditions of the induction motor 1, the secondary resistance r2 'changes by the temperature coefficient, and therefore K in the equation (4) changes, and for this reason,
The slip frequency fs also needs to be changed accordingly. At this time, if the condition of equation (2) is applied to the current as well,

[0016]

[Equation 3] Therefore, if s is controlled so that I1 becomes constant, it is possible to correct the characteristic change of r2 ′ due to the temperature change in the equation (3).

However, in the extremely low frequency region where the condition of the expression (2) is not satisfied, the drop due to the primary resistance r1 becomes large, and it is necessary to correct this. For this purpose, a predetermined torque can be obtained by outputting a voltage V that is a predetermined starting current Is with respect to a preset slip frequency reference value fs. In such a case, Since it is not possible to output a voltage in a predetermined pattern, it is necessary to freely control the voltage in the asynchronous mode.

[0018]

However, although such a conventional control method is based on the equivalent circuit shown in FIG. 8, it is actually a T-type equivalent circuit as shown in FIG.
Here, γ _m is an exciting resistance and x _m is an exciting inductance. The exciting voltage is affected by r ₁ and x ₁ , and even if V / f is constant, the amount of magnetic flux inside the induction motor is not constant, and further varies depending on the magnitude of the starting current I _s .
There is a problem that a predetermined torque is not obtained even if a predetermined starting current is applied and the starting acceleration is insufficient, or conversely, the torque is too large and the vehicle slips.

In the asynchronous mode, the primary resistance drop is also corrected, but since the slip frequency f _{s is} fixed, the change in the induced voltage due to the secondary resistance change is not corrected. As a result, the rotor temperature is high. At times, the current input to the excitation circuit increases, the induced voltage increases above a predetermined value, the amount of magnetic flux inside the induction motor increases, the starting torque becomes large, and slippage easily occurs. Conversely, when the rotor temperature is low, There was a problem that torque could not be obtained.

Further, at the point of switching from the asynchronous mote to the synchronous mode, the generated torque changes abruptly depending on the starting current and the rotor temperature, which causes a problem that the riding comfort of the electric vehicle becomes poor.

The present invention has been made in view of the above circumstances.
An object of the present invention is to provide a control method and a control device for an induction motor that can always obtain a predetermined starting acceleration, hardly generate slip, and perform control without causing deterioration of riding comfort.

[0022]

As a means for solving the above problems, the present invention, when driving an induction motor with the output of a PWM inverter, changes the modulation factor in the asynchronous mode to fix the slip frequency, In the induction motor control in which the modulation rate is fixed and the slip frequency is varied in the synchronous mode, the magnetic flux density at a predetermined location of the induction motor is detected,
On the basis of this detection, the slip frequency reference value in the asynchronous mode and the modulation rate reference value in the synchronous mode are corrected.

[0023]

In the above structure, the internal magnetic flux density of the induction motor is directly measured, the reference value of the slip frequency is corrected in the asynchronous mode from the difference between the measured value of the magnetic flux density and the set value of the magnetic flux density, and in the synchronous mode. Corrects the reference value of the modulation rate.

Therefore, even if the internal magnetic flux density fluctuates due to the influence of the primary resistance and the secondary resistance of the induction motor, the output of the inverter can be changed corresponding to this fluctuation, and a desired torque can be obtained. You can

[0025]

Embodiments of the present invention will be described below with reference to FIGS. However, the same components as those in FIG. 5 and FIG. 6 are designated by the same reference numerals, and the duplicated description will be omitted.

FIG. 1 is a control block diagram according to an embodiment of the present invention in the asynchronous mode. 1 is different from FIG. 5 in that a Hall element 16 as a magnetic flux density sensor, a gain constant circuit 17, a low pass filter 18, an adder 19,
The point is that a setter 20 for setting the magnetic flux density set value B _o and a gain constant circuit 21 are added. The Hall element 16, the gain constant circuit 17, and the low pass filter 18 constitute a magnetic flux density detecting means.

Next, the operation of FIG. 1 will be described. In the asynchronous mode, the current command value is I _s , the slip frequency forward value is f _so , and the magnetic flux density set value is B _o . Therefore, the modulation rate γ
And the output of the inverter 2 operating at the frequency f, the internal magnetic flux density B _s ′ of the induction motor 1 is measured by the Hall element 16 as a magnetic flux density sensor. Then, the gain constant circuit 17 having the predetermined conversion ratio K _B and the low-pass filter 18 can obtain the magnetic flux density B _{s in} which the fluctuation due to the transient fluctuation is eliminated.

The adder 19 uses this B _s and the magnetic flux density set value B
The deviation ΔB from _o is output. The gain constant circuit 21 calculates the slip frequency correction amount Δf _sB from the deviation _{ΔB according} to a predetermined conversion ratio K _fB . The adder 14 subtracts this slip frequency correction amount Δf _sB from the slip frequency reference value f _so to obtain the slip frequency set value f _s . The adder 10, the rotor rotational frequency f _r, adding the slip frequency setting value f _s during power running, regeneration time is _{subtracted, f = f r ± (f} so - △ f sB) ... (6 ) (However, ± is output at the time of power running: + at the time of regenerative operation :-) and outputs the reference frequency f of the inverter 2.

Thus, for example, even if the rotor temperature becomes higher than the planned value, the secondary resistance increases, the current flowing to the exciting circuit side increases, the induced voltage increases, and the magnetic flux density inside the induction motor increases. , The slip frequency f _s is reduced by the slip frequency correction amount Δf _sB , and the secondary resistance r ₂ ′ / s is equivalently reduced. Therefore, the induced voltage is lowered to the predetermined magnetic flux density set value B _o , and the torque is not excessive and the slip does not occur.

On the contrary, even if the rotor temperature becomes lower than the planned value and the secondary resistance decreases, the current flowing to the exciting circuit side decreases, the induced voltage decreases, and the magnetic flux density inside the induction motor decreases, the slip The frequency correction amount Δf _sB becomes a negative value, the slip frequency f _s increases, and the secondary resistance r ₂ ′ is equivalently increased.
/ S increases. Therefore, the induced voltage is increased to the predetermined magnetic flux density set value B _o , and the torque is not insufficient and the acceleration is not generated.

FIG. 2 is a control block diagram according to the embodiment of the present invention in the synchronous mode. Point 2 is different from FIG. 6, a Hall element 16 serving as a magnetic flux density sensor, the gain constant circuit 17, a low pass filter 18, an adder 19, setter 20 for setting the magnetic flux density setting value B _o, the gain constant circuit 22 is This is an added point.

Next, the operation of FIG. 2 will be described. The adder 19 outputs the deviation ΔB through the same process as in the case of FIG. Gain constant circuit 22 calculates the modulation factor correction amount △ gamma _B from the deviation △ B by a predetermined conversion ratio Kγ _B. It is added to this modulation rate correction amount Δγ _B , and the value γ obtained thereby is output to the inverter 3 as the modulation rate.

By such control, for example, when the primary winding temperature becomes lower than the planned value and the current command value is lower than the planned value, the primary winding resistance drop becomes lower than the planned value. Therefore, even if the voltage of the excitation circuit rises and the magnetic flux density inside the induction motor increases, the modulation factor correction amount Δγ _B
Becomes a negative value, the random rate γ decreases, and the voltage decreases.
Therefore, the _velocity density B _s is set to the predetermined magnetic flux density set value B _o.
Since it can be made equal to, the torque will not become excessive and slip will not occur.

On the contrary, when the primary winding temperature is higher than the planned value and the current command value is higher than the planned value, the primary winding resistance drop becomes higher than the planned value, and apparently Even if the voltage on the side of the excitation circuit decreases and the magnetic flux density inside the induction motor decreases, the modulation rate correction amount Δγ _B becomes a positive value, the modulation rate γ increases, and the voltage increases. Therefore, in this case as well, the hourly speed density B _s can be made equal to the predetermined magnetic flux density set value B _o , so that the torque does not become insufficient and the speed does not occur.

FIG. 3 is an explanatory view showing a cross section of the stator core tooth portion of the induction motor 1. In this figure, 23 is a stator coil inserted in the stator core slot, 2
Reference numeral 4 is a stator core tooth portion, and 16a and 16b are a pair of Hall elements as sensors for detecting the gap magnetic flux density.

The Hall elements are connected in a harmony manner in consideration of the polarities of the stator windings so as to cancel the ripple due to the rotor slot. For example, as a combination of the number of slots of a stator and a rotor often used in an induction motor for a vehicle, four poles and three stators are used.
Consider the case of 6 slots and rotor 46 slots. At a certain time, the stator tooth No. with the Hall element 16a attached was
No. 1 of the stator tooth mounted with the Hall element 16b having a polarity opposite to that of No. No. 10 is the rotor tooth No. 12, No. 1
The center of 3 is located. Therefore, since the magnetic flux pulsation due to the rotor slot is in the opposite phase relationship, if the outputs of the Hall elements 16a and 16b are connected to the summation, it is possible to substantially cancel the magnetic flux pulsation due to the rotor slot.

By controlling the above-mentioned asynchronous mode or synchronous mode using the measured value of the magnetic flux density obtained in this way, it becomes possible to operate at a predetermined acceleration without excess or deficiency of torque. Therefore, it is possible to prevent the occurrence of slip and the deterioration of riding comfort.

FIG. 4 is an explanatory view showing the mounting position of the search coil 25 when the search coil is used instead of the Hall element as the sensor for detecting the magnetic flux density. As shown in the figure, the search coil 25 is wound further inside the stator coil 23. Although not shown, a buffer amplifier that receives the output of the search coil 25 and an integrator that integrates the output of the search coil received by the buffer bump are provided at predetermined positions.

Since a magnetic flux density almost proportional to the magnetic flux density on the gap surface of the induction motor is generated in the back of the iron core, if this magnetic flux density is B _c , the search coil output eb is

[0040]

[Equation 4] Becomes This output is received by the buffer amplifier and integrated by the integrator, so that the integrator output voltage ei is

[0041]

[Equation 5] Thus, an output voltage proportional to the magnetic flux density can be obtained. By controlling the asynchronous mode and the synchronous mode by using the measured value of the magnetic flux density obtained in this way, it becomes possible to operate at the prescribed acceleration without excess or deficiency of torque, as in the case of using the Hall element. Therefore, it is possible to prevent the occurrence of slip and the deterioration of riding comfort.

[0042]

As described above, according to the present invention, the actual magnetic flux density of the induction motor is measured, the slip frequency and the correction amount of the modulation rate are calculated from the difference between the set magnetic flux density, and the slip frequency reference value and Since the asynchronous mode and the synchronous mode are controlled by correcting the modulation rate reference value and obtaining the optimum slip frequency setting value and modulation rate setting value, acceleration failure and torque due to insufficient torque in the asynchronous mode and synchronous mode It is possible to prevent slip due to overrun. Further, since it is possible to suppress the torque shock that has been inevitable in the past when switching from the asynchronous mode to the synchronous mode, it is possible to improve the riding comfort of the electric vehicle.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an apparatus according to an embodiment of the present invention in an asynchronous mode.

FIG. 2 is a block diagram showing a configuration of a device according to an embodiment of the present invention in a synchronization mode.

FIG. 3 is an explanatory view showing a mounting state of Hall elements in the induction motor of FIG. 1 or FIG.

FIG. 4 is an explanatory diagram showing a mounted state of the search coil when a search coil is used instead of the hall element in FIG.

FIG. 5 is a block diagram showing a configuration of a conventional device in an asynchronous mode.

FIG. 6 is a block diagram showing a configuration of a conventional device in a synchronization mode.

7 is an explanatory diagram showing a general operation pattern of the induction motor shown in FIG. 5 or FIG.

8 is a simplified equivalent circuit diagram of the induction motor shown in FIG. 5 or FIG.

9 is an accurate equivalent circuit diagram of the induction motor shown in FIG. 5 or FIG.

[Explanation of symbols]

 1 induction motor 2 PWM inverter 16 Hall element (magnetic flux density detection means)

Claims (6)

[Claims] 1. An induction motor control in which, when an induction motor is driven by the output of a PWM inverter, the modulation rate is varied to fix the slip frequency in the asynchronous mode, and the modulation rate is fixed to vary the slip frequency in the synchronous mode. In the method, the magnetic flux density at a predetermined location of the induction motor is detected, and based on this detection, the slip frequency reference value in the asynchronous mode and the modulation rate reference value in the synchronous mode are corrected. Induction motor control method. 2. An induction motor control in which, when the induction motor is driven by the output of a PWM inverter, the modulation rate is varied to fix the slip frequency in the asynchronous mode, and the modulation rate is fixed to vary the slip frequency in the synchronous mode. In the device, a magnetic flux density detecting means for detecting a magnetic flux density at a predetermined portion of the induction motor, a deviation output means for outputting a deviation between a preset magnetic flux density set value and a detected value from the magnetic flux density detecting means. An induction motor control device comprising: a slip frequency reference value correction unit that corrects a slip frequency reference value in the asynchronous mode based on an output from the deviation output unit. 3. An induction motor in which, when the induction motor is driven by the output of a PWM inverter, the modulation rate is varied to fix the slip frequency in the asynchronous mode, and the modulation rate is fixed to vary the slip frequency in the synchronous mode. In the control device, a magnetic flux density detecting means for detecting a magnetic flux density at a predetermined portion of the induction motor, a deviation output means for outputting a deviation between a preset magnetic flux density set value and a detected value from the magnetic flux density detecting means. And a modulation factor reference value correcting unit that corrects the modulation factor reference value in the synchronous mode based on the output from the deviation output unit, the induction motor control device. 4. The induction motor controller according to claim 2 or 3, wherein the magnetic flux density at a predetermined portion of the induction motor is a gap magnetic flux density of the induction motor or a value which is substantially proportional to the gap magnetic flux density. An induction motor control device characterized in that it has a magnetic flux density of a portion thereof. 5. The induction motor control device according to claim 2, wherein the magnetic flux density detecting means includes a Hall element. 6. The induction motor control device according to claim 2, wherein the magnetic flux density detecting means includes a search coil.