JPS6352685A - Current limiting circuit of controller for induction motor - Google Patents

Abstract

PURPOSE:To execute the control of high stability, by changing a current limit in an acceleration area, over to a current limit in an constant output area, continuously and smoothly. CONSTITUTION:To the output terminal t2 of a first OP amplifier 15 on an acceleration are, the output of voltage clamped with the Zener voltage of a Zener diode 13 is directed. Negative voltage Va divided with a variable resistor 16 is added to voltage V2 corresponding to a current limit value in a constant output area, and the input of the voltage to a second OP amplifier 21 is provided, and the output of positive voltage(Va+V2)is generated. In the constant output area, to the output terminal t2 of the first OP amplifier 15, the output of zero voltage is directed. The only voltage V2 corresponding to the current limit value in the constant output area is directed to the second OP amplifier 21 for input, and the output of the only voltage V2 is generated. When the current limit value in an acceleration area is shifted to the current limit value in the constant output area, then the value is shifted continuously and smoothly.

Description

[Detailed description of the invention] [Object of the invention] (Industrial application field) The present invention is directed to an induction motor used when an induction motor is used in a loading machine and the induction motor is controlled by an inverter device. This invention relates to a current limit circuit for a control device.

(Prior technology) Generally, when an induction motor is used in a loading machine and controlled by an inverter device, especially for hoisting bars, in order to increase cargo handling efficiency, the machine operates at high speed for light loads and at low speed for heavy loads. It is desirable to use the induction motor efficiently at its rated output by operating it at

Therefore, as the performance required of an inverter device that performs control, so-called constant output control, which controls the speed of the induction motor according to the magnitude of the load, is desired. In other words, when hoisting, if the torque required by the load (equivalent to the secondary current of the induction motor) is less than the rated output, the
It is desirable to weaken the excitation current of the motor and perform constant output control of the induction motor at a speed that corresponds to the magnitude of the load.

Furthermore, since inverter devices generally used for material dumping machines must be able to control the output torque over the entire range, a vector control system is used for this type of application. This vector control is an induced electric current! V control is performed as a current vector including the magnitude (amplitude) and frequency phase of the current supplied to the II machine. Excitation main of induction motor 2i! (Equivalent to DC motor field '6J & current)
The aim is to independently control the current and the secondary current (equivalent to the armature current of a DC motor) to obtain 1-lux control performance comparable to that of a DC motor.

Therefore, when the induction motor A machine is operated in a constant output range, it is necessary to perform limit control on the secondary current of the induction motor at the rated current and to weaken the excitation current. Also, of course, when accelerating, it is necessary to apply a current limiter of 130-150% or more of the rated value and carefully lift the load.

As mentioned above, inverter devices used in hoisting and dumping machines require a current limit circuit in the acceleration region and a current limit circuit in the constant output region, and it is also necessary to switch the current limit. . Therefore, normally in this type of device, the acceleration range of the induction motor is 130 to
The configuration is such that a 150% secondary current limit circuit operates, and above the rated speed, the rated secondary current limit circuit operates in a constant output range of the induction motor.

(Problem to be solved by the invention) However, in the case of an induction motor, the supplied current element is
Since only the primary current is a vector combination of the excitation component and the secondary component, instantaneous switching of the current limit causes disturbance and makes it impossible to lift the load stably. Also, since the current limiter is determined by the speed feedback signal, for example, when hoisting 100% rated load, the speed will be hoisted at 100% speed, so in this case as well, the current limit will be different from the limiter in the constant output range and the limiter during acceleration. The presence of two limiters results in unstable operation, which has the disadvantage that stable and safe cargo handling cannot be performed.

An object of the present invention is to have a current limit circuit in an acceleration region and a current limit circuit in a constant output region, and to have a structure that allows smooth transition from the current limit in the acceleration region to the current limit in the constant output region, and to provide a highly stable current limit circuit. Moreover, it is an object of the present invention to provide a current limit circuit for a control device for an induction Wi-motor that allows safe cargo handling.

(Means for Solving the Problems) The current limit circuit of the induction motor control device according to the present invention is inductive! ! In a control system that uses the output signal of a speed sensor attached to the shaft end of an II machine as a speed feedback signal and controls the speed of an induction motor according to a speed command signal from a main controller, an induction type used in the control system 11
The current limit circuit of the IJ machine detects the speed of the induction motor based on the speed feedback signal, and when the detected speed is less than the rated speed, the induction motor is in the acceleration region of the induction motor.
#A current limit circuit during acceleration that limits the secondary current of the J machine to the allowable current of its induction motor, and a constant output that limits the secondary current of the induction motor to the rated current by setting the induction motor in a constant output range above the rated speed. a current limit circuit;
A switching current limit circuit that changes the secondary current limit of the induction motor at a constant amplification rate according to the rotation speed of the induction motor when switching from the secondary current limit in the acceleration region to the secondary current limit in the constant output region. It is characterized by the following structure.

(Function) In the current limit circuit of the induction motor control device according to the present invention, when shifting from the current limit value in the acceleration region of the induction motor to the current limit value in the constant output region, the voltage characteristics of the Zener diode and the increase in the OP amplifier are determined. There is a continuous and smooth transition depending on the width ratio. Therefore, when the induction motor is used for a loading machine, it is possible to carry out highly stable and safe loading and unloading operations.

(Embodiment) An embodiment of the present invention will be described below while comparing it with a conventional circuit based on the drawings. First, FIG. 3 is a general schematic block diagram when the induction motor 1 is used in a hoisting and dumping machine and is controlled by an inverter device.

In Fig. 3, 1 is an induction motor which is the drive source of the hoisting and dumping machine, and 2 is an induction motor! A speed sensor is attached to the shaft end of the jJ machine and outputs a speed feedback signal ω1, and 3 is a master controller that outputs a speed setting signal.

4 is the speed feedback signal ω7 from speed sensor 2
A speed control circuit 5 inputs the speed command signal from the main controller 3 and performs error amplification, and 5 inputs the speed feedback signal from the speed sensor 2 and the output signal of the speed control circuit 4, and the induction motor 1 If the speed is below, a secondary current limit signal of 130 to 150% of the rated value is set as the acceleration region, and if the speed is above the rated speed, the rated secondary current limit signal is set as the constant output region, and the speed is controlled within that range. A current limit circuit that outputs the output signal of the control circuit 4, that is, the secondary current command signal I2 of the induction motor 1.

6 inputs the secondary current command which is the output signal of the current limit circuit 5 and the speed feedback signal ω1 as a current vector including the magnitude (width) and frequency phase of the current supplied to the induction motor 1. This is a vector control circuit that controls the The vector control circuit 6 also has a function of automatically weakening the excitation current of the induction motor 1 if the torque required by the load, in other words, the secondary current command 12 which is the output signal of the current limit circuit 5 is less than the rated output. Contains.

7 inputs a current feedback signal obtained by detecting the current supplied to the induction motor 1 by a current detector 9, and a primary current reference signal I supplied to the induction motor 1, which is an output signal of the vector control circuit 6. The iu current control circuit 8 that performs current control is an inverter main circuit composed of semiconductor elements operated by the output signal of the current control circuit 7.

The operation of a control device for an induction motor for a load-throwing machine using such a circuit configuration will be briefly described. Note that the speed control circuit 4. Since the vector control circuit 6 and the current control circuit 7 are general, well-known circuits, detailed explanations thereof will be omitted. Now, when a speed command signal is input to the speed control circuit 4 by the master controller 3, it is compared with the speed feedback signal ω, and the speed control circuit 4 outputs a speed deviation signal. The speed deviation is.

This is the magnitude of the secondary current (torque component) necessary for the induction motor 1, and the polarity indicates the direction of the torque.

A speed deviation signal, which is an output signal of the speed control circuit 4, is input to a current limit circuit 5. A speed feedback signal ω is input to the current limit circuit 5, and as described above, if the speed feedback signal is below the rated speed, a secondary current limit signal of 130 to 150% of the rated speed is set as the acceleration region. Further, when the speed feedback signal is equal to or higher than the rated speed, the rated secondary current limit signal of the induction motor is set as a constant output region.

Therefore, the output signal of the current limit circuit 5 is limited by a limit value set in the acceleration region or constant output region. The secondary current command signal I8, which is the output signal of the current limit circuit 5, is subjected to vector calculation together with the excitation current reference signal in the vector controller ypr6, and becomes a primary current reference signal circuit 7 that is supplied to the induction motor 1. Therefore, the current flowing through the induction motor 1 is detected by the current detector 9, and this current base P! The main circuit conversion element 8 is controlled by comparing and amplifying the signal A, and the speed of the induction motor 1 is controlled.

For convenience of explanation, the output characteristics of the conventional current limit circuit 5 are shown in FIG. 4. The current limit value is plotted on X#, the speed is plotted on the Y axis, and if the speed is 100% or less, the current limit value during acceleration is shown. The current limit value is 130 to 150%, and has a characteristic that the current limit value switches to 100% when the speed becomes 100% or more.

Furthermore, for convenience of explanation, FIG. 5 shows an example of a conventional circuit for switching the current limit value.The comparator CP1 has a speed feedback signal ω, and a voltage reference value VS[! corresponding to the rated speed. T is input, the two signals are compared, and the subsequent analog switch A-3W is operated. A voltage v1 corresponding to the current limit value in the acceleration region and a voltage ■ corresponding to the current limit value in the constant output region are input to the analog switch A-8W, and when ωp < V sat, V is input by the output of the comparator CP1. =V,,ω1≧Vs
During RT, the configuration operates as ■=v2.

Therefore, the current limit value is switched by the speed feedback signal ω1, but as described above, instantaneously switching the current limit causes disturbance and makes it impossible to lift the load stably.

Now, one embodiment of the current limit circuit according to the present invention is shown in FIG. In Fig. 1, parts with the same functions as those in Fig. 5 are indicated by the same symbols.
input resistance, 11 is the voltage-based value corresponding to the rated speed vs
F! 7 is the input resistance of the first OP amplifier 15, and the input resistance 10.11 is the input resistance of the first OP amplifier 15]
612 connected to the inverting input terminal t0 of 5 is the first OP
A resistor connected to zero volt potential from the non-inverting input terminal ti of the amplifier 15.

14 is an inverting input terminal t of the first OP amplifier 15; The feedback resistor 13 of the first ○P amplifier 15 is connected to the output terminal t2 and the feedback resistor 14 in parallel, and its cathode is connected to the input terminal t. A Zener diode whose anode is connected to the output terminal t2.

A variable resistor 16 is connected to the output terminal t2 of the first OP amplifier 15 and zero volt potential, and divides the output voltage of the first OP amplifier 15.

Furthermore, 17 is the input resistance of the second OP amplifier 21 for the signal from the voltage v2 corresponding to the current limit value in the constant output region, and 18 is the input resistance of the second OP amplifier 21 for the output divided voltage of the variable resistor 16. and input resistance 17
．． 18 is connected to the inverting input terminal t□ of the second OP amplifier 21. 19 is a resistor connected to the non-inverting input terminal t4 of the second OP amplifier 21 and zero volt potential, and 20 is the non-inverting input terminal t3 of the second OP amplifier 21 and the output terminal t.
This is the feedback resistance of the second ○P amplifier 21 connected to 5.

Next, the operation of the current limit circuit of the present invention constructed in this manner will be described below. The speed feedback signal ω2 is a negative voltage, the voltage reference corresponding to the rated speed V 91! Select T to be a positive voltage and make the resistance values of input resistors 10 and 11 the same.

ω! ->VSET, a positive potential is likely to be output to the output terminal t2 of the first OP amplifier 15 due to the amplification factor of the input resistor 10.11 and the feedback resistor 14, but due to the forward characteristics of the Zener diode 13. Zero voltage is output.

Therefore, the output voltage v8 of the variable resistor 16 is zero voltage. Therefore, only the voltage v2 corresponding to the current limit value in the constant output region is input to the second OP amplifier 21, and if the resistance values of the input resistor 17, 18 and the feedback resistor 20 are selected to be the same, and v2 is set to a negative potential, then Only v8, which corresponds to the current limit value in the constant output region, is output to the output t of the OP amplifier 21 of No. 2.

Next, ωl−<VSF! At the time of T, a negative voltage is outputted to the output terminal t□ of the first OP amplifier 15 by the amplification factor of the input resistor 10.11 and the feedback resistor 14, and is clamped by the Zener voltage of the Zener diode 13.

A negative voltage va obtained by dividing the output voltage of the first OP amplifier 15 clamped by the Zener voltage by the variable resistor 16 is input to the second QP amplifier 21 through the input resistor 18 . Here, since ■2 is a negative potential, V and +Va are added and inputted to the second OP amplifier, and a positive voltage of Va+V2 is outputted.

If the variable resistor 16 is set so that V2+Va=Vt, a voltage v1 corresponding to the current limit value in the acceleration region, that is, when ωr<VsEt, is obtained.

In this way, the current limit value in the acceleration region and the current limit value in the constant output region can be obtained. When shifting from the current limit value in the acceleration region to the current limit value in the constant output region, the voltage characteristics of the Zener diode 13 and the O
The amplification factor of the P amplifier 15 causes a continuous and smooth transition.

Figure 2 shows the amplification factor of the first OP amplifier 15 equal to 1 of the rated speed.
This shows the input/output characteristics when ~2% is selected, and the voltage value corresponding to the current limit value is shown at X@.

This shows the velocity feedback signal ω on the y-axis. As can be understood from FIG. 2, the transition from the current limit value in the acceleration region to the current limit value in the constant output region is continuous and smooth. Therefore, a loading machine using such a current limit circuit can operate stably.

〔Effect of the invention〕

From the above explanation, if the current limit circuit according to the present invention is used, it has a current limit circuit in the acceleration region and a current limit circuit in the constant output region, and switching from the current limit in the acceleration region to the current limit in the constant output region is continuous. The inverter device using this current limit circuit can perform highly stable and safe cargo handling.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a current limit circuit of the control device for an induction motor of the present invention, Fig. 2 is a characteristic diagram of the current limit circuit, and Fig. 3 is a control device for a general induction motor for a hoisting machine. FIG. 4 is a characteristic diagram of a conventional current limit circuit, and FIG. 5 is a circuit diagram showing a conventional current limit circuit. 1...Induction@Motive 2...Speed sensor 3...
Main controller 4...Speed control circuit 5...Current limiter circuit 6...Vector control circuit 7...Current control circuit 8.
...Inverter circuit 10, 11.17.18...Input resistor 13...Zener diode 14.20...Feedback resistor 15...10th P amplifier 16...Variable resistor 21...
...20th P amplifier agent Yoshiaki Inomata (and 1 other person) Fig. 1 (130-150°/) Fig. 2 Fig. 3 Fig. 4 130-150'/.

Claims (1)

[Claims] (1) In a control system that uses the output signal of a speed sensor attached to the shaft end of an induction motor as a speed feedback signal and controls the speed of the induction motor according to a speed command signal from a master controller, The current limit circuit of the induction motor detects the speed of the induction motor based on the speed feedback signal, and when the detected speed is less than the rated speed, the secondary current of the induction motor is set as the acceleration region of the induction motor. a constant output current limit circuit that limits the secondary current of the induction motor to the rated current by setting the induction motor in a constant output range above the rated speed; and a constant output current limit circuit that limits the secondary current of the induction motor to the rated current when the speed exceeds the rated speed. A current limit circuit for an induction motor control device comprising a switching current limit circuit that changes the secondary current limit of the induction motor at a constant amplification rate according to the rotation speed of the induction motor when switching to the secondary current limit of the region. circuit.