JPH0584156B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a control device for an induction motor driven by an inverter using a slip frequency type vector control system. It is concerned with removing the influence of values.

[Prior Art] In recent years, an inverter drive system using vector control has been frequently adopted as a method for controlling the speed of an induction motor to the same level as a DC motor.

FIG. 4 is a block diagram showing a conventional control device for this type of induction motor.

In the figure, 1 is a three-phase AC power supply, 2 is a rectifier circuit composed of diodes, etc. that obtains DC voltage from this three-phase AC power supply, 3 is a DC voltage smoothing filter,
4 is an inverter circuit composed of switching elements such as transistors, 5 is an induction motor as a load (hereinafter simply referred to as "motor"), 6 is a speed detector,
7 is a speed command circuit that provides a speed reference for the electric motor 5;
Reference numeral 8 denotes a speed detection circuit that calculates the motor speed from the output signal of the speed detector 6, and 9 receives the deviation between the output signal ω _ref of the speed command circuit 7 and the output signal ω _r of the speed detection circuit 8 as input, and calculates the torque component current. A compensation circuit whose output is i〓 _qs , 10 is the output i〓 _qs of the compensation circuit 9 and a command current i〓 ₁ based on calculations of excitation component current i〓 _ds , command rotation speed ω _p , etc. from the output i〓 _qs of the compensation circuit 9 and the motor rotation speed ω r. 11 is a reference sine wave command forming circuit that outputs a reference sine wave waveform for PWM control based on the output of the command current _i〓1 of the vector calculation circuit 10, 12
13 is a current detection circuit that detects the bus current of the inverter, and 13 is a pulse that generates a signal to turn on and off the switching elements of the inverter circuit 4 based on the deviation between the output of the reference sine wave command forming circuit 11 and the output of the current detection circuit 12. It is a width modulation (PWM) control circuit.

In vector control configured in this way, the power supply current is divided into two current components: a current i 〓 _ds that generates a secondary magnetic flux rotating inside the motor 5, and a current i _qs that generates a torque perpendicular to the current i 〓 _ds . In order to control the coordinates by converting the _{coordinates into} A method of calculating the sum and integrating it (slip frequency type vector control method) is used. This calculation method is based on the following three basic vector calculation equations (a), (b), and (c).

Motor torque: T _M = M/L ₂・i〓 _qs・Φ ₂ Secondary magnetic flux: Φ ₂ (s) = M/1 + L ₂ /R
₂ S・i〓 _ds (S)...(b) Slip frequency: ω _S = R ₂ M/Φ ₂ L ₂・i〓 _qs ...(c) Here, M: Mutual inductance of the motor L ₂ : Motor Secondary inductance R ₂ : Secondary resistance of the motor The above equation (a) is an equation related to torque, equation (b) is an equation related to secondary magnetic flux, and equation (c) is an equation related to slip frequency.

Therefore, the magnitude of the torque to be applied to the electric motor 5 is determined from the difference between the command speed and the motor rotation speed, and the i〓 _qs and i〓 _ds necessary to generate that torque can be found from (a) and (b). .

Also, the slip frequency can be found from equation (c). Therefore
Speed control can be performed by applying the current of equation (d) to the motor 5.

i ₁ =√｜i〓 _qs ｜ ² +｜i〓 _ds ｜ ² ×sin {(ω _s + ω _r )
t+θ} However, θ=tan ^-1 |i〓 _qs |/|i〓 _ds | ...(d) That is, the above equations (a) to (d) are obtained from the vector calculation circuit 10, and the vector calculation circuit 10's Command current i ₁
The inverter circuit 4 is controlled based on the output of the motor 5, and the electric motor 5 is driven and controlled.

[Problems to be Solved by the Invention] Incidentally, in the above equations (a) to (c), the mutual inductance M of the electric motors 5 and the secondary inductance _L2 of the electric motor 5 are constant, but the secondary inductance of the electric motor 5 The value of the resistance R ₂ changes depending on the temperature.

Temperature and actual secondary resistance in motor 5 in Figure 3
To illustrate its influence using an explanatory diagram showing the relationship with R′ ₂ in the form of current, as a result of the vector calculations in equations (a) to (c) above, the excitation current is supplied from the inverter circuit 4 to the motor 5. Even if it is assumed that the current component i〓 _ds-1 and the torque component current i〓 _qs-1 are calculated, and the current I ₁ (in other words, the torque of the area of the downward-slanted area to the right) is applied to the motor 5, the If the value of the secondary resistance _R'2 differs from the actual value, the position of the secondary magnetic flux will not be determined correctly, and the motor 5 will have a change in the secondary resistance _R'2 due to temperature, for example, as shown in the figure. An excitation current i _ds-M and a torque component current i _qs-M flow as supply currents, and the current I ₁ becomes a torque corresponding to the area of the diagonally lined portion upward to the right.

Therefore, it is necessary to perform some kind of temperature correction on the secondary resistance R ₂ to reduce the phase shift |θ〓−θ _M |.

However, conventional devices do not have a circuit to compensate for temperature changes in the actual secondary resistance R′ ₂ , and the value of the secondary resistance R ₂ , which does not affect normal use, is set by trial and error. , electric motor 5
The problem is that when the set value of secondary resistance R ₂ and the actual value of secondary resistance R′ ₂ differ greatly, such as when the secondary resistance R 2 is cold or overheated, the specified torque is not produced. The dot was hot.

Therefore, this invention was made to solve the above problems, and it is possible to determine the inverter output from the inverter bus voltage and bus current without installing a special device such as a temperature detector inside the motor. The object of the present invention is to provide a control device for an induction motor that can correct the temperature of the secondary resistance by compensating for the deviation from the command output, and as a result has a high response.

[Means for Solving the Problems] The induction motor control device according to the present invention detects the output of the inverter circuit, corrects the secondary resistance based on the magnitude relationship with the command output, and adjusts the timing of the correction. This method utilizes changes in the magnitude of the torque component current command.

[Function] In this invention, since the fluctuation of the secondary resistance value is corrected based on the detection signal when the absolute value of the torque component current command is larger than the absolute value of the magnetic flux component current command, the predetermined It is possible to generate torque and perform control with high stability and responsiveness.

[Embodiment] Hereinafter, a control device for an induction motor according to an embodiment of the present invention will be described. Note that in the drawings, the same reference numerals and symbols as those in the conventional example indicate constituent parts that are the same as or correspond to the constituent parts in the conventional example, and thus redundant explanation will be omitted here.

In FIG. 1, 14 is an inverter output detection circuit that detects an inverter output P based on the average value of the bus voltage V _DC and bus current i _DC of the inverter circuit 4 to the motor 5, and 15 is a command output from the vector calculation circuit 10. Find P ^* and inverter output detection circuit 14
This is an input resistance correction circuit that corrects the secondary resistance _R2 based on the deviation from the output of the input resistance R2. In addition, 16 is a threshold detection circuit that detects that the absolute value of the torque component current command i〓 _qs is larger than the absolute value of the magnetic flux component current command i〓 _ds in order to determine the timing of correction. It consists of a comparison circuit that takes one input. 17 is a secondary resistance correction switch which receives the detection signal and performs ON/OFF control.

Here, the threshold value detection circuit 16 of this embodiment presets the threshold value i 〓 _{qs -nax} of the torque component current command i〓 qs determined by conditions such as the inverter capacity and the capacity of the electric motor 5, and Current command i〓 _qs is its threshold value i〓 _qs-nax
In the above case, a detection signal indicating that "i〓 _qs is greater than a threshold value" is output, and the switch 17 is turned ON only when this signal is output.

That is, the secondary resistance correction circuit 15 operates only when the torque component current command i〓 _qs is equal to or greater than the threshold value, and based on this, the vector calculation circuit 10 operates to adjust the secondary resistance.
Correct R ₂ .

Inverter output detection circuit 14 in this embodiment
FIG. 2 shows a detailed configuration between the secondary resistance correction circuit 15 and the secondary resistance correction circuit 15. Incidentally, in the figure, the bus current and bus voltage can be digitized by using the A/D converter 19, and assembled using software using a microprocessor.

In FIG. 2, 18 is a current detector using a Hall element or the like, which detects the inverter bus current. Reference numeral 19 constitutes a temporary delay circuit consisting of an A/D converter that receives the output of the current detector 18 and converts it into digital data, a CR filter, and the like. A voltage detector 20 detects the inverter bus voltage. 21 is an A/D converter which receives the output of the voltage detector 20 with an insulated amplifier or the like and converts it into digital data; 22 is a multiplier.

The multiplier 22 generates the detection output P as follows: P=V _DC ×i _DC average value, where V _DC = bus voltage of the inverter circuit i _DC = bus current of the inverter circuit.

24 is a secondary resistance compensation circuit which is composed of P control or PI control, and whose time constant is set to be equal to the thermal time constant of the electric motor 5, and the correction amount △R ₂ is obtained as its output. Therefore, use the value added or subtracted from the preset input resistance value R ₂ as the secondary resistance R ₂ ←R ₂ ±△R ₂ of the motor 5,
It is used for vector calculation by the vector calculation circuit 10. The correction amount △R ₂ at this time is the secondary resistance R ₂
It is possible to divide the design value, which changes with a predetermined temperature rise, into n, and use the value of 1/n as the correction amount ΔR ₂ .

25 is a multiplier. The inverter output command P ^* is determined by the multiplier 25 as P ^* =k×ω _r ×T T=k′×i _qs ×i _ds , so that P ^* =k1×ω _r ×i _qs ×i _ds , k = proportionality constant [2π/60g≒1.0269] k' = proportionality constant (determined by the motor) k1 = k x k' ω _r = motor rotation speed [rpm] T = torque [Kg・m].

Therefore, when the electric motor 5 is determined, the inverter output command P ^* is determined depending on the rotation speed when the electric motor is driven.
is found. In addition, 23 is a gain adjustment circuit that adjusts the command output and absolute amount by its gain.
Match the units corresponding to the first proportionality constant K1.

In addition, in the configuration shown in Figure 1, the actual secondary resistance
R ₂ increases with increasing temperature, resulting in
As can be understood from FIG. 3, if there is a difference between the secondary resistance R ₂ on the control device and the secondary resistance R ₂ ' of the actual motor 5, the output becomes the input to the secondary resistance correction circuit 15. The deviation △P is as follows: △P=P ^* −P = (torque command value) × k × ω _r − (actual output torque) × k × ω _r = {｜I〓 ₁ ｜sinθ〓・｜I〓 ₁ ｜ cosθ〓 −｜I〓 ₁ ｜sinθ _M・｜I〓 ₁ ｜cosθ _M ｝ ×k×ω _r = {｜I〓 ₁ ｜ ² sinθ〓cosθ〓 −｜I〓 ₁ ｜ ² sinθ _M cosθ _M }×k ×ω _r =｜i〓 ₁ ｜ ² sinαcos (2θ〓−α) ×k×ω _r However, α＝θ〓−θ _M ……(e) When a large torque is output during acceleration/deceleration, etc. If limited, there is a relationship between the torque component current command i〓 _qs and the magnetic flux component current command i〓 _ds as |i〓 _qs |＞|i〓 _ds |, and 90°＞θ〓＞45°, And 2θ〓−α=θ
〓
Since +θ _M ≒2θ〓, when torque is required such as during acceleration/deceleration (when the torque component current is larger than the threshold value), 180°>2θ〓−α>90°, and cos(2θ〓−α)＜ It becomes 0.

Therefore, when △P>0, sinα<0, therefore α<0, so reduce the value of the secondary resistance R ₂ ,
When △P<0, sinα>0, therefore α>0, so the value of the secondary resistance R ₂ should be increased,
Based on this, the secondary resistance correction circuit 15 sends out an output. The reason why it is possible to correct the secondary resistance R ₂ in this way is that |i〓 _qs | depends on the operating conditions of the induction motor.
If ＞｜i〓 _ds | is satisfied, that is, if more than a certain amount of torque is generated, the polarity of △P and the deviation between the calculated value R ₂ and the actual value R ₂ ′ of the secondary resistance This is because there is a correlation with the polarity of

Note that (actual output torque)×k×ω _r is equivalent to the inverter output, and can be detected by the average value of the bus voltage V _DC and the bus current i _DC .

That is, in this embodiment, the inverter circuit 4
Inverter output P is detected based on the average value of bus voltage V _DC and bus current i _DC , and inverter output command P ^* is calculated based on torque component current command i〓 _qs and magnetic flux component current command i〓 _ds . Since ^the initially set secondary resistance _{R 2} is corrected based on the relationship _with Since 〓−α)＜0, the polarity of α can be determined from the polarity of △P, and the magnitude relationship between the calculated secondary resistance R ₂ and the actual secondary resistance R ₂ ′ of the motor 5 can be determined. _The secondary resistance R ₂ is corrected so that 1im t→∞(P-P ^* )=0.

In this case, the cos(2θ〓−α)<0 condition holds.
Based on the value of i〓 _q-nax , I〓 _qs > i〓 When _q-nax , the secondary resistance R
₂
Correct.

As described above, the induction motor control device of this embodiment is based on the torque component current command i〓 _qs , the magnetic flux component current command i〓 _ds , and the motor circuit speed ω _r due to the deviation between the speed reference value and the detected speed value. In an induction motor control device for controlling an induction motor 5, which includes a vector calculation circuit 10 that performs vector control calculations and sends out an output command, and a pulse width modulation control circuit 13 that controls an inverter circuit 4 based on the output command. , an inverter output detection circuit that detects an inverter output from the bus voltage and bus current of the inverter circuit, and a threshold detection circuit that detects that the absolute value of the torque component current command is larger than the absolute value of the magnetic flux component current command. and, based on the detection signal from the threshold detection circuit, when the inverter output command value from the vector calculation circuit is larger than the inverter output detection value from the inverter detection circuit, the secondary resistance of the induction motor is reduced. , and a secondary resistance correction circuit that sends a correction value to be increased when the resistance is small to the vector calculation circuit.

Therefore, the bus voltage V _DC of the inverter circuit 4
The inverter output P is detected based on the _average value of the bus current i 〓 _qs and the bus current i 〓 _qs , and the inverter output command ^P actual secondary resistance
Determine the change in R′ ₂ . In other words, the torque component current command
When i〓 _qs is a predetermined threshold signal, correction for the variation in the secondary resistance R ₂ is repeated, so the actual variation in the secondary resistance R′ ₂ due to temperature can be detected without using a special resistance measurement detection means. In addition to being able to make corrections, a predetermined torque can be generated to perform control with high safety and responsiveness, and a stable and highly responsive induction motor control device can be obtained.

In the above embodiment, the threshold detection circuit 16 determines the operation timing of the secondary resistance correction based on the threshold detection signal of the torque component current, but in addition to the torque component current, the threshold detection signal of the command current i〓 ₁ Similar functionality can be achieved using .

[Effects of the Invention] As described above, according to the induction motor control device of the present invention, the inverter output is detected based on the average value of the bus voltage and bus current of the inverter circuit, and the inverter output is detected based on the average value of the bus voltage and bus current of the inverter circuit. Since the change in secondary resistance is determined based on the relationship with the inverter output command, which is determined by calculation based on the divided current command,
Fluctuations in the actual secondary resistance of the induction motor due to temperature can be corrected without using special measuring means. Therefore, the effect is that a predetermined torque can be generated and control with high stability and responsiveness can be performed without being affected by temperature changes, and a stable and highly responsive induction motor control device can be obtained. There is.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a control device for an induction motor according to an embodiment of the present invention, and FIG. 2 is a detailed internal block diagram for correcting secondary resistance in the control device for an induction motor according to an embodiment of the present invention. 3 is an explanatory diagram showing the relationship between temperature and secondary resistance in an induction motor, and FIG. 4 is a block diagram of a conventional induction motor control device. In the figure, 4...Inverter circuit, 5...Induction motor, 6...Speed detector, 7...Speed command circuit, 10...Vector calculation circuit, 11...Reference sine wave command formation circuit, 13...Pulse Width modulation control circuit, 14... Inverter output detection circuit, 15...
Secondary resistance correction circuit, 16...threshold value detection circuit, and the same reference numerals in the drawings indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A vector calculation circuit that performs vector control calculation and reversely outputs an output command based on a torque component current command and a magnetic flux component current command based on a deviation between a speed reference value and a detected speed value; and a pulse width modulation control circuit that controls an inverter circuit based on the inverter output detection circuit that detects an inverter output from a bus voltage and a bus current of the inverter circuit; a threshold detection circuit that detects that the absolute value of the torque component current command is greater than the absolute value of the magnetic flux component current command; and an inverter output command value from the vector calculation circuit based on the detection signal from the threshold detection circuit. is larger than the inverter output detection value from the inverter detection circuit, the secondary resistance of the induction motor is made smaller, and when it is smaller, the correction value is sent to the vector calculation circuit to increase it. A control device for an induction motor, comprising a circuit.