JPS58127595A - Current limiting circuit for inverter - Google Patents

Abstract

PURPOSE:To readily suppress the excess current of an inverter by suppressing the slip and the output voltage only when the load current flows over the prescribed value. CONSTITUTION:When the load current of an inverter 4 increases larger than the set value, this is detected by a current detector 15, and the output signal I of the detector 15 is inputted together with the output omegaS of the amplifier 9 to a frequency correcting circuit 16. The output of the detector 15 is inputted also to a voltage correcting circuit 17, which produces an output when it becomes higher than the current limiting value, this output signal is inputted to a voltage instructing circuit 11, so that the output of the circuit 11 decreases in th value lower than the current limiting value instantaneously at the prescribed rate to the ordinarily operating value. When the current I recovers to the value lower than the current limiting value, the output of the circuit 11 gradually recovers to the ordinary value.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current control circuit for an inverter device whose load is an AC motor.

A conventional example of a slip frequency control type variable voltage variable frequency inverter device using an induction motor as a load will be explained below based on FIGS. 1 to 3. Figure 1 shows Pu1a Wid-th Modulat
ion (hereinafter referred to as PWM) voltage-controlled type Inno-4-Y is a schematic block configuration diagram. In the diagram, it! Three-phase AC commercial power supply, 2 is a rectifier R circuit composed of diodes or thyristors, etc. that obtain a DC voltage tube from this three-phase AC power supply %3#i DC voltage smoothing filter, 4 is composed of switching elements such as transistors Imper 2 circuits, 5
#i Load AC motor, 6 company operation detector, 7 is a speed command circuit that provides a parallel reference tube for the load motor 5, 8 is a speed detection circuit that amplifies the output signal of the speed detector 6, 9 is a speed command The output signal ref of the circuit 7 and the output signal ω of the speed detection circuit 8
The sum signal of the output signal #8 of the slip frequency signal amplifier 10 and the output signal ω of the speed detection circuit 8, that is, the frequency command signal A voltage/Δlus converter that outputs a pulse train with a proportional frequency; 11 is a voltage command circuit from the above No. 04 that outputs a voltage level that matches the V/F characteristic of the load motor 5; 12 is a voltage command circuit that outputs a voltage level corresponding to the V/F characteristic of the load motor 5; A base voltage waveform forming circuit that receives an input and outputs a reference voltage waveform Yt ratio for PWM control; 13 is a voltage detection circuit that detects the output voltage of the inverter; 14ti
12 reference voltage waveform forming circuit output and voltage detection circuit 43
This is a PWM control circuit that creates a signal to turn on and off the switching element tube of the inverter circuit number based on the deviation from the output of the inverter circuit.

The m2 diagram shows the torque and electric R relative to the rotational speed of the induction motor.
This is a graph showing the case where the vehicle is operated in a force state with a load torque TCt.

Here, N is the rotational speed of the electric motor, and C is the synchronous rotational speed. ω, that is, the output signal ω of the frequency signal amplifier 9.

It is designed to correspond to Due to the function of the slip frequency signal amplifier 9 shown in Figure 1, when the rotational speed fN of the motor is about to change as the load torque TL changes, the output signal ω of the frequency signal amplifier 9 changes.

changes, and as a result, ω・, that is, the synchronous rotational speed N・ is adjusted in the transverse direction t, the speed of the motor! [Nt - Operates to keep constant. In addition, for overload, the output clamp device II is installed in the slip frequency signal amplifier 9! Let's hold it together
Normally, the load motor current is suppressed from increasing beyond a certain value determined by the characteristics of the motor. Figure 3 shows an example of mt in which the load torque TL increases, %ω increases, and the flang value ωamaxK.
The current is limited to +0.

However, when the speed suddenly changes, such as during acceleration/deceleration in q#, during a transition between power and regeneration, and during forward/reverse operation.

Because the inverter frequency suddenly changes (-3 suddenly changes.

As a result, ω・ suddenly changes), and due to the transient phase difference n between the haze electromotive voltage and the inverter output voltage,
A current of more than ... flows. In other words, there is a transient current jump phenomenon. Ninth, conventionally, the current jump phenomenon has been suppressed by suppressing the rate of change of ω to below a certain value, but the response of the inverter device was poor and it could not withstand severe use.

The present invention was made in view of the above-mentioned circumstances, and it is an object of the present invention to provide a current control @ circuit for an inverter device that is stable and highly responsive without transient current jump even when the speed suddenly changes as described above. It has nine purposes.

Embodiment 1 of the present invention will be described in detail below based on Figures 1m4 to 17m. In the drawings, parts and parts corresponding to those of the conventional example are given the same reference numerals, and explanations thereof will be omitted.

Figure 4 shows an example 1/IA of the present invention! This is a lock diagram, and 15, 16, and 17 are added to the conventional example shown in FIG. 1. 15 A current detector detects the load current of the inverter, 16 is a frequency correction circuit, and the output signal of the current detector 15 and the output ml of the slip frequency signal amplifier 9 are input. , has a dead zone of the current limit value Iox for the I signal, and is configured such that a signal having the same sign as ωB is output and subtracted from f′L%ω6.

In addition, 17 is a voltage correction circuit that generates an output when the output of the current detector 15 is inputted to n% or more (Iox),
This output signal is input to the voltage command circuit 11, and is configured such that the output of the voltage command 11 decreases instantaneously, sometimes by a constant ratio, with respect to the steady-state operating value. Further, the circuit is configured such that when the current I returns to below Iox, the output of the voltage command circuit 11 gradually returns to a steady value with a certain time constant.

In the inverter device according to the present invention configured as described above, when the current exceeds the current limit value 1ox tube at the time of sudden load change RrL, the inverter output frequency f and output voltage V become It instantly decreases from the operating value at at, and the motor current rapidly decreases. As a result, 11
As shown in FIG. 7, when the motor #i decreases below IOX, the inverter output frequency returns to its steady value, and the output voltage also returns to its steady value later than n.

Here, by gradually returning the output voltage, an increase in current due to a transient phase shift n when the inverter output frequency returns to a steady value is also suppressed.

Also, during regeneration, the inverter output frequency f increases instantaneously, and the output voltage V decreases, and after the current is restored, it returns to the steady value as in the case of power. In this way, excessive current rI
By quickly suppressing L and acting only when the current limit value exceeds n1, stable and reliable operation is guaranteed without impairing steady-state responsiveness.

Incidentally, in the above overview, a case has been described in which the current detector 15t is configured on the inverter output side, but it goes without saying that even if it is configured as 15' on the DC side, a valuable effect can be expected.

As described in detail above, according to the present invention, the configuration is simple, and the output voltage is controlled to be suppressed only when the load current flows beyond a predetermined value.
Easily suppresses excessive current without sacrificing responsiveness.
This has the effect of providing a stable and highly reliable inverter device.

[Brief explanation of drawings]

a! Fig. 1 is a schematic block diagram of a conventional slip control type PWM voltage control type inverter device, Fig. 112 and Otori Fig. 3 are torque and current characteristics diagrams with respect to rotational speed of an induction motor, and Fig. 4 shows an embodiment of the present invention. A block diagram of the inverter device, FIG. 5 is a diagram showing an example of the output characteristics of the total frequency correction circuit,
! [Figure 6 is a diagram showing an example of the output characteristics of the voltage correction circuit, I
Figure L7 is a diagram showing the operation of the circuit according to the present invention. 1... Three-phase AC power supply %2... Rectifier,
3... Smoothing filter, 4... Inverter device, 5... River/load AC motor, 6...
・Speed detection @%7... Speed generation command circuit, 8...
...Speed detection circuit %9...Slip frequency signal amplifier, 10...Voltage//4 pulse converter, 11
...... Voltage command circuit %12... Reference voltage waveform forming circuit %13... Voltage detection circuit, 14.
...PWM control circuit%15,15'...
Current detector, 16... Frequency correction circuit, 17.
...Voltage correction circuit. Patent applicant Mitsubishi Electric Corporation agent
Makoto Kuzuno - (1 other person) Figure 2 and Figure 3 (7 Figure 5 Eka Figure 7 Procedural amendment (voluntary) ↑, ¥Xu Commissioner's Palace 1, Incident display Patent application Sho 1f-7! Snow・Taste 2,
Name of the invention: Inverter eccentricity 0@Takiseizen-ro 3, Person making the amendment Representative: Hitoshi Katayama Department 4, Agent 3; "A simple explanation of one drawing in the Iji specification @column 10", "Drawing J. Contents of correction (1) @Specifications ms page 7th line, tlr where it says "--Load torque Tct"i... Correct the load torque T&t=J. (2) Ibid. JL [Page 3, line 8, "Run in N-power state..." is corrected to read "Run in power running state -1." (3) Ibid. JL, page 17, line 17. , r-ms diagram is turbid liquid total correction...'' is corrected as r-...Figure 5, Hiro frequency correction...j. (4) Amend Figures 2 and 3 of the IIWO compilation as attached. )a

Claims (1)

[Claims] In an inverter device that uses an AC motor as a load, when the load current increases above a set value, this is detected and the inverter frequency is fully increased or decreased to reduce the slip of the AC motor, while at the same time suppressing the output voltage. When the load current falls below the set value, the power is turned on/? - A current w@ circuit for an inverter device, comprising: a frequency correction circuit for restoring a motor frequency to a normal control value; and a voltage correction circuit for gradually restoring an output voltage with a delay from the frequency restoration.