JPS649839B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improving the acceleration/deceleration characteristics of a slip frequency control device for an induction motor.

A conventional device of this type is shown in FIG. In the figure, 1 is an AC power supply, 2 is a converter for obtaining variable voltage DC from the AC power supply, and 3 is a converter for obtaining variable voltage DC from the AC power supply.
is an inverter for converting direct current to variable frequency alternating current, 4 is a smoothing reactor, 5 is an induction motor, 6 is a torque current command to the induction motor, 7 is an excitation current command, 8 is a torque current command 6, an excitation current command 7 8A is the output signal of the calculator 8, 9 is the current detector for feedback, 9A is the output signal of the current detector 9, 10 is the current controller, 11
12 is a phase control circuit; 12 is an arithmetic unit for outputting the optimum phase difference between the secondary magnetic flux and the primary current of the motor based on the values of the torque current command 6 and the excitation current command 7;
2A is the output of the calculator 12, 13 is a speed detector for detecting the speed of the motor, 13A is the output of the speed detector 13, 131 is a pulse transmitter that outputs a pulse signal with a frequency proportional to the speed of the motor, 13
2 is a converter for converting the signal from the pulse transmitter 131 into an analog voltage signal proportional to the motor speed, and 13B is a converter that converts the signal from the pulse transmitter 131 into an analog voltage signal proportional to the motor speed.
The motor primary frequency command obtained by adding 6A (proportional to I _T ^* ), 14 is the motor primary frequency command 1
Integrator for integrating 3B, 14A is integrator 1
The output signal 4 commands the momentary integrated phase of the output current of the inverter 3 when there is no torque fluctuation, and the output signal 15 commands the secondary magnetic flux and primary current of the motor according to the amount of torque change. The amount of phase shift 12A required to produce the optimal phase difference between
This signal is the final amount that commands the momentary integrated phase of the output current of the inverter 3, even when there is torque fluctuation. 16 is signal 1
This is an inverter control circuit for controlling the output current integration phase of the inverter 3 according to the command No. 5.

Figure 1 shows what is called a slip frequency control type vector controller, and the magnitude of the motor primary current is √ _T ^*2 + ^*2 /Kc (where Kc is the motor's primary current,
Coupling ratio between secondary components)...(Equation 1) The integrated phase of the motor primary current is ∫ ^t _p (ω _n +K _T・I _T ^* )dt+tan ^-1 (I _T ^* /Im ^* ) (However,
ω _n : synchronous angular frequency corresponding to the actual speed of the motor,
It is widely known that an induction motor can be operated at the same high performance as a DC motor by controlling it so that K _T : proportionality constant) (2nd formula). The arithmetic unit 8 is for calculating the first equation and outputs a command 8A, and the arithmetic unit 12 is for calculating the second term of the second equation. Also, ω _n in the second formula is the synchronous frequency 13A in Figure 1, K _T・I _T ^* is all the required frequency 6A, ω _n +K _T・I _T ^* is the motor primary frequency command 13B, and the second formula The first term corresponds to the signal 14A, and the entire second equation corresponds to the signal 15. Current controller 10, current detector 9, phase control circuit 1
The current control loop consisting of 1 controls the motor primary current (equal to the inverter output current and power supply current) to match the value of the first equation, that is, the command 8A, and the inverter control circuit 16 controls the integrated phase of the motor primary current (equal to the inverter output current and the power supply current) (equal to the integrated phase of the output current) is controlled to match the value of the second equation, that is, the signal 15.

When controlled as described above, an ideal vector diagram in an actual electric motor becomes as shown in FIG. FIG. 2 shows the relationship between various quantities expressed on coordinates fixed to the rotating secondary magnetic flux. In the figure, φ ₂ is the secondary magnetic flux,
Im is the actual value of the excitation current to create φ ₂ (the above
Im ^* ), I _T is the actual value of the torque current (distinguished from I _T ^* above), and the secondary magnetic flux φ ₂
It is perpendicular to φ2, and generates a torque proportional to the product of _φ2 . The torque current I _T flows due to the speed electromotive force generated by cutting the secondary magnetic flux φ ₂ . As a result, the magnitude of I _T is expressed as the speed at which the secondary conductor cuts the secondary magnetic flux φ ₂ , that is, a function of the slip frequency ωs and φ ₂ , and I _T =Kωsφ ₂ (3rd equation). . (Here K is a proportionality constant). Further, the relationship between Im and φ ₂ is the relationship between the excitation current and the magnetic flux generated thereby, and is expressed as Im=f(φ ₂ ) (4th equation).
(f: nonlinear function) Now, when the motor primary current I ₁ is applied from the inverter, the motor secondary current I ₂ will flow, decreasing by the coupling ratio between the motor 1 and the secondary. However, with this alone, it is not possible to determine how much of each of the excitation current Im and the torque current I _T can be distributed. It is only determined that point A in FIG. 2 is on the circumference of a circle whose diameter is I ₂ . If ωs is determined here, the third and fourth equations are functions of only φ ₂ , and by eliminating φ ₂ from both equations, another relational expression between Im and I _T can be obtained, as shown in Figure 2. The position of point A is determined. Therefore, torque current command I _T ^* ,
Actual torque current value faithful to excitation current command Im ^*
The value of ωs is an important element in order to obtain I _T and the actual excitation current value Im, and to create an ideal control state. If the value of ω _n in the second equation is ideal, the slip frequency ωs matches K _T · _IT ^* in the second equation. If there is an error in ω _n , the slip frequency actually applied to the motor will be K _T · I _T ^* + Δω _n . (Δω _n :error of ω _n ). When operating near the rated speed, generally K _T・I _T
^* is a value of about 1 to 2% of ω _n . Therefore, ω _n
If the accuracy is poor, it will greatly affect the slip frequency. When the slip frequency becomes small due to an error in ω _n , over-excitation occurs, and when the slip frequency becomes large, under-excitation occurs.

As described above, the characteristics of the device shown in FIG. 1 are influenced by the detection accuracy of ω _n . Therefore, a highly accurate speed detector 13 in FIG. 1 is used, but depending on the detection method, even if the steady state detection accuracy is good, it may have an inherent detection delay time. In this case, for example, when the actual speed changes as shown by the solid line in FIG. 3, the detected speed changes as shown by the broken line. In the figure, Δt is the detection delay time, and Δω _n is the speed detection error that occurs during acceleration and deceleration due to Δt. Note that the relationship Δω _n =motor acceleration×Δt (5th equation) holds between Δω _n and Δt. Due to this Δω _n , the slip frequency during acceleration and deceleration becomes smaller than necessary, causing the motor to be over-excited and resulting in a deterioration in characteristics.

This invention was made to eliminate the above-mentioned drawbacks, and aims to improve the acceleration/deceleration characteristics of a slip frequency controlled induction motor by compensating for speed detection errors during acceleration/deceleration of the motor.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 4 shows an embodiment of the present invention, in which only a portion corresponding to the speed detector 13 in FIG. 1 is shown. The other configurations are the same as those in FIG. In the figure, 131 is a pulse transmitter that outputs a pulse with a frequency proportional to the speed as in FIG. A device that counts the number of pulses and outputs it as an analog output, 132A is its output, 13
3 is a filter provided for noise removal as necessary, 134 is a differentiation circuit, 134A is the output of the differentiation circuit 134, and 13A is the output 132A and output 1.
This is a signal obtained by adding 34A. In the device configured in this way, in FIG. 4, 1
The path 32→132A→13A corresponds to the conventional device shown in FIG. 1, and has the aforementioned speed detection error during acceleration/deceleration, and the error Δω _n is as shown in equation 5. On the other hand, the path consisting of 132→133→134→134A is an acceleration/deceleration error calculation circuit. If the time delay Δt of the converter 132 is always constant, from the fifth equation, Δω _n ∝motor acceleration = dω _n /dt (sixth equation), and the detected speed ω _n is differentiated by the differentiator 134. It can be seen that the required correction amount can be found by .

This correction amount 134A is used as the conventional speed detection signal 13
2A, a new speed detection signal 13A is obtained. This signal can indicate the current actual speed of the motor even during acceleration/deceleration, and the fourth
If the speed detector 13 shown in the figure is replaced with the speed detector 13 shown in FIG. 1, slip frequency control with good characteristics without overexcitation even during acceleration or deceleration can be performed.

Although the above embodiments have mainly been described with respect to analog circuits, it goes without saying that the present invention can also be applied to digital control.

As described above, according to the present invention, even when a speed detector with a time delay is used, it is possible to prevent speed detection errors during acceleration/deceleration from occurring due to the speed detector, and to realize an induction motor with good controllability. Slip frequency control is possible.

[Brief explanation of drawings]

Fig. 1 is a control block diagram showing an example of a conventional device, Fig. 2 is a vector diagram to explain the device in Fig. 1, and Fig. 3 is an operation waveform to explain the operation of the device in Fig. 1. 4 are block diagrams of a speed detector showing an embodiment of the present invention. In the diagram, 1... AC power supply, 2... converter, 3
...Inverter, 4...Smoothing reactor, 5...
Induction motor, 6...torque current reference, 6A...required slip frequency, 7...excitation current reference, 8...computer, 8A...motor primary current command, 9...current detector, 9A...current detection device output, 10... Current controller, 11... Phase control circuit, 12...
Arithmetic unit, 12A...Arithmetic unit output, 13...Speed detector, 131...Pulse transmitter, 132...Converter, 132A...Converter output, 133...Filter, 134...Differential circuit, 134A... ... Differential circuit output, 13A ... Speed detection signal, 13B ... Motor frequency command, 14 ... Integrator, 14A ... Integrator output, 15 ... Inverter output current integration phase command, 16 ... Inverter control circuit, In the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. An inverter that is supplied with power from a variable voltage DC power source and converts DC into variable frequency AC, an induction motor that receives the variable frequency AC from the inverter, a speed detector that detects the speed of the induction motor, and the induction motor. an integrator that integrates the primary frequency command, an arithmetic unit that outputs an optimal phase difference between the secondary magnetic flux and the primary current of the induction motor based on the values of the torque current command and the excitation current command, and an output of the integrator. A control device for an induction motor includes a control circuit for the inverter that receives as input a signal added to the output of the arithmetic unit, and a pulse transmitter that outputs pulses proportional to the speed of the induction motor, and inputs the pulses. A speed detection converter with a certain detection delay, a differentiating circuit that inputs the output of this speed detecting converter via a filter, and an adder for the output of this differentiating circuit and the output of the above speed detecting converter. A control device for an induction motor, characterized in that the speed detector comprises: