JPH072039B2 - Sliding angular frequency correction method - Google Patents

Description

The present invention relates to a slip angular frequency correction method for a torque control device for an induction motor.

Conventionally, there has been a torque control device for an induction motor shown in FIG. In Fig. 1, 1 is the specified torque Tr
Is a torque command generator that generates a torque command value Tr, and a torque current (signal) that has a predetermined correspondence with this command value Tr
Circuit for generating a Aitau, circuitry for generating the excitation current (signal) I _E by the rotation speed N is 3, 4 _1, 4 _2, 4 ₃ the torque current Aitau
And exciting current I _E , input the current I
A circuit 5 for generating signals of an absolute value I _{M of M} (ω, θτ), a phase θτ and a slip angular frequency ω _s is a slip angular frequency (signal) ω _{s in} which the slip angular frequency ω _s is corrected by an operation described later. A circuit for generating ′ inputs the rotational angular frequency ω _m included in the rotational speed N, and the current I
_A drive circuit for obtaining _M (ω, θτ), 7 is a current I _M (ω, θ)
An induction motor driven by τ), that is, a motor, 8 is a detector that detects the rotation of the motor 7 and generates a rotation speed N.

Here, the circuit 4 ₁ ～4- ₃ is a circuit that performs arithmetic processing shown by the following equation.

θτ = tan ^-1 · (Iτ / _IE ) (2) Where R ₂ is the resistance of the secondary winding of the motor 7 and L ₂ is the motor 7
Is the inductance of the secondary winding.

FIG. 2 is a vector diagram showing the above relationship in vector form. When the exciting current I _E is plotted on the horizontal axis and the torque current I τ is plotted on the vertical axis, the absolute value I _M becomes a combined vector of them and moves on the vertical axis with respect to changes in the torque current I τ.

Further, the current I _M (ω, θτ) output from the drive circuit 6
Is Is. However, ω = ω _m + ω _s Due to such a relation, the steady-state condition after the torque change is completely satisfied, and the torque τ of the motor 7 and the slip are small when there is almost no change in the magnetic flux with respect to the rotor of the motor 7. The angular frequency ω _s and the torque current I τ maintain a linear proportional relationship with each other, and the torque τ of the motor 7 is the current I _M (ω, θ
τ). In this way, the device exhibits a linear response to the specified value Tr. In addition, the weakening control of the air gap magnetic field (weak magnetic field control) is performed by the exciting current of the circuit 3.
It can be done by I _E.

However, the characteristics as described above are established only when the resistance R ₂ does not change with temperature or the like, and in the actual case, the resistance R ₂ changes with temperature, so that the exciting current I _E and the torque current I τ are changed. Is also affected by changes in temperature. Therefore, due to the change in temperature, the motor 7
Changes the magnetic flux even with a steady load, and also causes an error in torque.

For this reason, the circuit 5 is provided as a correction circuit as shown in FIG. 1, and the slip angular frequency ω _s is corrected by the following equation.

FIG. 3 is a block diagram showing the details of the circuit 5 that realizes the equation (5), and is configured to obtain the operation of the equation (5). That is, the circuit 9 detects the super power E _m of the motor 7,
10 generates a command value E _m 'of a motor 7, the circuit 11 by entering detects deviation Delta] E _m, the deviation Delta] E resistance by correcting the value R ₂₀ at a reference temperature of the resistor R ₂ by _m R ₂ ’, And Is multiplied by the slip angular frequency ω _s in the circuit 12 and output as ω _s ′.

For example, if the temperature of the motor 7 is t ° C. and the resistance R ₂ is 75 ° C., Becomes

Normally, the actual slip angular frequency ω _s ′ is calculated by the equation (5) by the correction represented by the equation (6), and the motor 7 is controlled in the corrected state. In this state, the temperature change Δt of the resistor R ₂
Considering the above, the characteristics of the motor 7, the command value and the actual value of the exciting current I _E or the torque current I τ change, and the super power E _m changes. As a result, the device controls the deviation ΔE _m at the input of the circuit 11 to zero, and finally the motor 7 settles in some steady state.

The conventional torque control device for the electric motor is configured as described above, and the slip angular frequency is corrected to cope with the temperature change of the resistance of the secondary winding of the motor in the operating state.
Immediately after the activation, the correction is not performed, and the electromotive force _Em becomes a small value in the low speed region, so that there is a drawback that a detection error is likely to occur.

This invention was made in order to eliminate the above-mentioned drawbacks of the conventional ones, by estimating the temperature rise of the secondary winding from the secondary copper loss, and by correcting the slip angular frequency with the result, An object of the present invention is to provide a slip angle frequency correction method for a torque control device for an induction motor, which can correct a torque control error due to a temperature change even when restarting after a short stop or in a low speed range.

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 4, (20) is a squarer, and the circuit (2)
The torque current Iτ is received from and the square value Iτ ² of the torque current is calculated. (21) is a secondary copper loss calculator (multiplier) that multiplies the output of the squarer (20) and the output of the adder (27). The output of the adder (27) is the ratio (rate of change) R _2t of the resistance value R _2t ″ of the secondary resistance R ₂ after the temperature change and the resistance value R _{20 at} the reference temperature (zero degrees in this embodiment). ″ / R ₂₀
Is the content. (22) is a subtractor, (30) is an integrator, and (23) is an amplifier, and these constitute a first-order lag system (24) having a first-order lag characteristic described later, and the motor (7)
The voltage corresponding to the ratio ΔR ₂ / R ₂₀ of the resistance change ΔR ₂ and R ₂₀ of the secondary resistance R ₂ due to the heat generation due to the secondary copper loss of is output.
The subtractor (22) performs an operation of subtracting the output of the amplifier (23) from the output of the secondary copper loss calculator (21), and with respect to the torque current Iτ {output of (2)} shown in FIG. Then, the output {output of (22)} of an alternating waveform whose absolute value gradually decreases is emitted. Reference numeral (25) is a temperature sensor for measuring the ambient temperature t ° C inside the induction motor (7). (Usually, the exhaust temperature is measured, and the air temperature in the air gap between the stator and rotor of the induction motor is measured.) (26) is a calculator, which is a temperature sensor (25).
The following equation is calculated and output based on the ambient temperature t ° C. detected by.

However, R _20: the reference temperature the resistance value R _2t secondary resistance R ₂ in (0 ° C. in this embodiment) ': ambient temperature t two at ° C. primary resistance R ₂ of the resistance value alpha _0: temperature coefficient (27) An adder, which adds the output of the first-order lag system (24) and the output of the computing unit (26) and inputs the output having the content of R _2t ″ / R ₂₀ to the circuit (12). For configuration,
Since it is the same as that of FIG. 1, its description is omitted.

The integrator (30) is constructed as shown in FIG.

In the figure, (31) is an absolute value circuit, and an adder (2
Output the absolute value waveform of the output in 2). Reference numeral (32) is a voltage controlled oscillator, which generates a pulse having a frequency proportional to the level of the input absolute value waveform. Reference numeral (33) is a polarity detection circuit, which outputs logical value signals of "H" and "L", respectively, when the polarity of the output of the adder (22) is positive and negative. (35) and (36) are AND circuits, the former inputs the pulse to the addition terminal UP of the calculator (up / down counter) (37) while the logic value signal is "H", and the latter , The pulse is input to the subtraction terminal DOWN of the calculator (37) while the logic value signal is "L". (34) is an inverter. The output of the calculator (37) is converted into an analog signal by the D / A converter (38) and output to the amplifier (23). In this way, the integrator (30) integrates the input whose magnitude gradually decreases with time, so that an output that increases or decreases with the first-order lag characteristic is generated. FIG. 6 shows the output waveforms {outputs of (22) (31) to (38) (23)} of the elements forming the first-order delay system (24). This integrator (30) has a configuration in which the input is digitally converted and integrated. However, this is because the time constant of the temperature rise of the secondary circuit of the induction motor (7) is very large, and in the analog amplifier This is because the problem of drift arises.

Next, the operation of this control device will be described. First, when a torque designated value Tr is given and a corresponding torque current Iτ is output from the circuit (2), a secondary copper loss calculator (multiplier)
From (21) Is output. In vector control induction motor (7),
Since the secondary current flowing in the secondary winding is proportional to the torque current Iτ, the temperature change rate of the torque current Iτ ² and the resistance R ₂ The product of P _L and P _L is proportional to the secondary copper loss.

This secondary copper loss causes the secondary winding to generate heat and rise in temperature, but in an induction motor in which forced draft cooling is performed, the temperature rise width _Δt of the secondary winding is proportional to the secondary copper loss, and It has been experimentally confirmed that the characteristics are approximated by the first-order lag characteristics. The first-order lag system (24) of the embodiment imitates the temperature characteristic by adjusting the gain of the amplifier (23), that is, the time constant of the system, and outputs the rate of resistance change shown in the following equation.

In the initial state of the induction motor, the induction motor secondary current Iτ {(2) output} is zero, and the output P _L {(8) expression of the secondary copper loss calculator (21) in FIG. 4 is expressed. } Becomes zero. The output of the first-order delay system (24) is zero as an initial value.

The output of the adder (27) when the specified torque Tr is given in the condition that the ambient temperature is t ₁ ° C Then, the resistance value R _2t ″ of the secondary resistance R ₂ when the temperature of the secondary winding is (t ₁ + Δt) is obtained, and the angular velocity ω _s is calculated by the circuit (1
In 2) Is corrected as follows. That is, the correction is made based on the ambient temperature t ₁ ° C and the temperature increase Δt ° C due to the heat generation of the secondary winding.

The correction is performed based on the ambient temperature t ₁ ° C and the temperature increase Δt ° C due to the heat generation of the secondary winding in this way for the following reason.

That is, first, considering the structure of the induction motor, the temperature of the secondary-side resistance to be obtained, which is composed of a stator and a rotor as is well known, is determined as follows.

(A) The temperature sensor (25) in FIG. 4 normally measures the exhaust gas temperature and detects the air temperature in the air gap between the stator and the rotor. It is known from heat conduction engineering that the temperature of the secondary winding arranged on the rotor is determined by the sum of the temperature change of the structure (rotor body) that uses the secondary circuit copper loss as a heat source. .

When the temperature t ₁ ° C of the air gap is detected, the temperature t ₂ ° C of the secondary winding arranged on the rotor becomes a heat source P because the secondary winding itself has copper loss, and the secondary winding and the air Since there is a thermal impedance (first-order lag characteristic) Z between the gaps, t ₂
= T ₁ + ZP

This is the rate of change in resistance at ambient temperature t ₁ ° C. And rate of change in resistance due to temperature rise due to heat generation of secondary winding ZP = Δt ° C With the addition of It corresponds to becoming.

It is the temperature correction factor of the secondary resistance R _2. Is a function of the secondary copper loss and is given by calculation,
Even when the induction motor (7) is stopped for a short time and restarted or operated at a low speed, the function as the temperature correction factor is not lost and the complementary temperature value is reliably given.

That is, in the initial state when the induction motor is started Is zero, Exists, and due to the time constant of the first-order lag system (24), when restarting even if stopped halfway, the stop period is up to about twice the time constant of the first-order lag element (24). , Can be considered to have a valid output, rather than zero, so in the very initial state Is zero but restarts after a short stop Has a valid output.

In this embodiment, since the temperature characteristic of the secondary resistance R ₂ is simulated by the first-order lag system (24), extremely accurate temperature correction is performed, and very highly accurate torque control is realized.

Although the command value of the torque component current is used for the calculation of the secondary copper loss in the above embodiment, it goes without saying that the same effect can be obtained even if the measured value of the secondary current is used. Further, when the induction motor is not of the forced ventilation type, the gain of the first-order lag system may be corrected according to the rotation speed.

As described above, according to the present invention, the secondary copper loss is first proportional to the torque current command or the amount of the secondary current squared and the secondary resistance value at the reference temperature corrected by the induction motor internal temperature.
2nd secondary resistance change rate Δ with respect to the secondary resistance value at the reference temperature calculated from the above copper loss in the secondary resistance change rate R _2t ′ / R ₂₀
The second secondary resistance change rate ΔR ₂ / R ₂₀ is obtained by multiplying by the amount obtained by adding the values of R ₂ / R _{20 and} the second-order copper loss is derived through the first-order lag element, The slip angular frequency is corrected by being multiplied by the amount obtained by adding the values of the first secondary resistance change rate R _2t ′ / R ₂₀ and the second secondary resistance change rate ΔR ₂ / R _20. Therefore, the induction motor has a short time (first-order lag element (24)
(Up to about twice the time constant of) The temperature of the secondary resistance is reliably corrected even when the motor is stopped and restarted or at low speed, and the slip angular frequency is controlled so that the induction motor generates torque according to the specified torque. Therefore, over a wide operating range of the induction motor,
Highly accurate torque control can be performed.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a conventional torque control device for an induction motor,
2 is a current vector diagram of the torque control device, FIG. 3 is a circuit diagram of a slip angle frequency correction circuit of the device, and FIG. 4 is a torque control of an induction motor to which the slip angle frequency correction method according to the present invention is applied. FIG. 5 is a circuit diagram of an embodiment of the apparatus, FIG. 5 is a circuit diagram of the integrator in the above embodiment, and FIG. 6 is an operation waveform diagram of each part of the above embodiment. The same reference numerals in the drawings indicate the same or corresponding parts. In the figure, (1) ... torque command generator, (2) ...
Circuit for generating torque current, (20) …… Square multiplier, (21)
…… Secondary copper loss calculator, (22) …… Subtractor, (23) …… Amplifier, (24) …… Primary delay system element,… (25) …… Temperature sensor, (26) …… Operation unit, (27) …… Adder, (30)…
… Integrator, (31) …… Absolute value circuit, (32) …… Voltage controlled oscillator circuit, (33) …… Polarity detector, (34) …… Inverter, (35), (36)… And circuit , (37) …… Counter, (38) …… D / A converter.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-57-20189 (JP, A) JP-A-53-36622 (JP, A) JP-A-56-86089 (JP, A)

Claims (1)

[Claims] 1. A torque current command, an excitation current command, and a rotation speed of an induction motor are introduced to supply a current I _M to the induction induction motor, a phase θτ, a slip angular frequency ω _s , and a rotational angular frequency ω _m. Is derived, and a slip angle frequency correction method for a torque control device for an induction motor that supplies power to the induction motor based on the current I _M , the phase θτ, the slip angular frequency ω _s , and the rotation angular frequency ω _m to control the drive is obtained. Where, the secondary copper loss is the squared value of the torque current command or the squared value of the secondary current, corrected by the internal temperature t of the induction motor to obtain the secondary resistance value R _2t ′ and the secondary resistance value at the reference temperature. The secondary resistance value ΔR calculated and derived from the first secondary resistance change rate (R _2t ′ / R ₂₀ ) which is the ratio to R ₂₀ and the secondary copper loss through the primary delay element. ₂ and a second secondary resistance change ratio where the ratio of the secondary resistance value R ₂₀ at a reference temperature [Delta] R ₂ / R ₂₀₎ together with the determined by multiplying the added value and, in the slip angular frequency of the first secondary resistance change rate and the second
The method of correcting a slip angle frequency is characterized in that the correction is performed by multiplying by a value obtained by adding the secondary resistance change rate.