JPS60249897A - Rotating speed controller of induction motor - Google Patents

Abstract

PURPOSE:To prevent an induction motor from stalling by providing a stall preventing circuit having an overcurrent detector and an overvoltage detector, thereby setting the starting time to short time and eliminating the overvoltage and overvoltage trip. CONSTITUTION:An overcurrent detector 6 for detecting whether a current flowed through an inverter 4 to an induction motor 8 is an allowable current or higher, and an overvoltage detector 7 for detecting whether a regenerative voltage from the motor 8 is an allowable voltage or higher or not are provided. A stall preventing circuit 9 having gate circuits A1, A2 for controlling the alterations of the voltage and the frequency in a controller by the outputs of the both detectors is provided. Thus, even if the load is not constant, it can eliminate the starting time to become much longer, and the overvoltage and overcurrent grip to prevent the motor from stalling.

Description

[Detailed Description of the Invention] [Technical Field 1] The present invention relates to a rotational speed control device for an induction motor, which controls the rotational speed by changing the frequency of a driving AC power source and operates at a constant torque by changing the voltage. It is something that flashes in my mind.

[Background Art] Conventionally, this type of rotation speed control device that controls the rotation speed of an induction motor by converting the frequency of an AC power source and also changes the voltage to perform constant torque operation is shown in Fig. 12. Ta. In the figure, 1 is a 3-phase AC power supply, 2 is an AC power supply 1
3 is a voltage regulator that chops the DC power output from the converter 2 to make the DC power supply voltage variable, and a chopping transistor Q
, choke coil CH, flywheel guide D7, smoothing capacitor C, and chopper control circuit CO.
1 and a comparator CP1, and a chopping trannostar Q. The DC power supply voltage output from the voltage regulator 3 is set to a predetermined value based on the control input from the control circuit 5 by controlling the on/off duty of the voltage regulator 3. Reference numeral 4 designates an inverter which generates an AC power source for driving an induction motor at an appropriate frequency by manually inputting the output of the voltage regulator 3, and includes switching transistors Q, to Q6 having gate electrodes connected in antiparallel, a switching control circuit CO2, and a control circuit 5. It is formed with a /F conversion circuit VF that generates a frequency proportional to the control input voltage from the voltage regulator 3, and is controlled by turning on and off the DC power output from the voltage regulator 3 with switching trannostars Q, ~Q. Generates three-phase AC power at a predetermined frequency based on the input.

Here, the switching transistors Q1 to Q6 of the inverter 4 are turned on and off under PWM control to generate a sinusoidal AC power source. Reference numeral 5 denotes a control circuit that controls the voltage regulator 3 and the inverter 4 based on the rotation value set in the rotation speed setting section made of Polyureum VR, and sets the voltage and frequency of the AC power output from the inverter 4 to predetermined values. There is an oscillation circuit O8, an up-down counter UD that counts the output of the oscillation circuit OS, a rag network RN that generates a control voltage based on the output of the up-down counter UD, and a volume control output that outputs the count of the up-down counter UD. and a comparator CP that controls based on the ladder network RN output, and a voltage regulator 3.
And the voltage and frequency of the AC power supply applied to the induction motor 8 are gradually changed by gradually increasing or decreasing the control voltage that controls the inverter 4 to the control voltage corresponding to the rotation speed set by the polyureum VR. The rotation speed is controlled in consideration of the inertia of the induction electric motor Fp18.

By the way, in such a conventional example, the increasing control speed and decreasing control speed of the rotation speed of the induction motor 8, which are set by the oscillation frequency of the oscillation circuit O8, that is, the acceleration/deceleration time of the induction motor 8 are optimally set according to the load. However, when the load is not constant, if the acceleration/deceleration time is set long to account for load fluctuations, it will take too long to start. If it is set too short, there is a problem that an overvoltage or overcurrent trip occurs and the induction motor 8 stops. That is, when the load is not constant, it is extremely difficult to shorten the startup time and prevent the induction motor from stalling.

[Object of the Invention] The present invention has been made in view of the above points, and its purpose is to
An object of the present invention is to propose a rotational speed control device for an induction motor that can set a short startup time and prevent stalls by preventing overvoltage and overcurrent tripping.

[Disclosure of the Invention] (Embodiment) Fig. 1 shows an embodiment of the present invention, in which an inverter 4 is shown. an overcurrent detection circuit 6 that detects whether the current flowing through the induction motor ε(
A date circuit consisting of an overvoltage detection circuit 7 that detects whether the regenerative voltage from the rain detection circuit 6. When the output of the overcurrent detection circuit 6 is obtained, the output of the AND circuit A1 becomes L level, and the down counter tJD is forced to the down count side. Also, when the overvoltage detection circuit 7 output is obtained, the AND circuit A2 output becomes I- level and the up/down counter tJD is forcibly stopped counting, thereby increasing the voltage and frequency in the control circuit 5. Changes are controlled to prevent stalls. In the figure, R is a current detection resistor.

The operation of the embodiment will be specifically explained below.

Now, when the rotation speed setting is changed using the volume VR, the current rotation speed and the set rotation speed are compared by the comparator CP2, and the output of the comparator CP1 selects the associative count 1 and down count of the amplifier down counter IJD. It is selected whether to increase or decrease the rotation speed. For example, induction electric FpX8
When increasing the rotation speed of the comparator CP2
When the output is at I level, the rear 7 down counter UD goes up to count up, and the 7 down counter UD goes up.
ID counts up the pulses outputted from the oscillation circuit O8. Therefore, the control voltage output from the lag network RN, which generates a voltage based on the output of the amplifier down counter UD, increases stepwise (for each clock pulse count), and the voltage regulator 3
As the DC voltage output from the
The switching frequency of the inverter 4 gradually increases, and the rotation speed of the induction motor 8 gradually increases. Induction electric 8!
When the rotation speed of the 8 becomes higher than the set rotation speed, the comparator CP2 output becomes L level, the amplifier down counter UD is set to down count, and the control voltage output from the Lugkin 1 work RN becomes low. The rotation speed of the induction motor 8 is lowered. .

Therefore, the rotational speed of the induction motor 8 is gradually increased until it reaches the rotational speed set by the volume VR, and the motor enters steady operation. It should be noted that the operation during the lowering operation of the rotational speed is the same as the operation during the above-mentioned increasing operation (only the counting operation of the amplifier down counter UD is reversed), so a detailed explanation will be omitted.

By the way, when the load connected to the induction motor 8 is constant and the acceleration/deceleration time of the induction motor Wi 8 with respect to the load is optimal, the power supply voltage and frequency of the AC power supply applied to the induction motor 8 Since the rotational speed of the induction motor 8 changes in accordance with the change in The voltage is also below the allowable value. Therefore, the output of the overcurrent detection circuit 6 and the output of the overvoltage detection circuit 7 are both at the IJ level, and the operation of the control circuit 5 is exactly the same as in the conventional example.

On the other hand, if the load connected to the induction motor Σ) is unstable and the acceleration/deceleration time of the induction motor 8 relative to the load becomes inappropriate, a current exceeding the Jγ tolerance value will flow through the inverter 4. If the regenerative voltage from the induction motor 8 exceeds the allowable value, the overcurrent detection circuit 6 output or overvoltage detection circuit 7 output is obtained, and the rain detection circuit 6.7 output is applied to the induction motor 8. Changes in the voltage and frequency of the AC power source are controlled, and acceleration/deceleration times are adjusted to prevent stalls. That is, in the process of gradually increasing the rotation speed, the load connected to the induction motor 8 becomes heavier, and the control speed for increasing the rotation speed (the speed of increase in the voltage and frequency of the AC power supply applied to the induction motor 8) increases. When the actual rotational speed of the induction motor 8 cannot follow the L increase speed, the current flowing through the inverter 4 becomes significantly large, the output of the overcurrent detection circuit 6 becomes L level, and the output of the AND circuit A1 becomes When the level becomes low, the amplifier down counter UD is forcibly switched to down-counting, and the control voltage output from the ladder network RN is lowered to limit the current flowing to the induction motor 8 via the inverter 4 to below a permissible value. This prevents the induction motor from stopping due to overcurrent F-ramp. Also, in the process of lowering the rotation speed,
When the load connected to the induction motor 8 becomes lighter and the actual rate of decrease in the rotational speed of the induction motor 8 cannot follow the rate of decrease in the rotational speed, the regenerative voltage from the induction motor 8 becomes significantly high ( As a result, the output of the overvoltage detection circuit 7 becomes 1- level, the output of AND circuit A2 becomes L level, and the clock pulse input to the amplifier down counter UD is forcibly stepped and output from the ladder network RN. The control voltage is stopped from decreasing and the regenerative voltage is prevented from increasing, thereby preventing the induction motor 8 from stopping due to an overvoltage trip.

As described above, in the present invention, when the load on the induction motor 8 fluctuates and the acceleration/deceleration time becomes inappropriate, the current flowing to the induction motor 8 via the inverter 4 or
Since the acceleration/deceleration time is adjusted to fl when the regenerative voltage from
Furthermore, even if the startup time is set short, stalls due to overvoltage and overcurrent trips can be prevented.

[Effects of the Invention] As described above, the present invention includes a converter that rectifies an AC power source and outputs a DC power source, a voltage regulator that chops the DC power output from the converter and makes the DC power source voltage variable; An inverter receives the voltage regulator output and generates AC power for driving the induction motor at an appropriate frequency, and an AC output from the inverter by controlling the voltage regulator and impark based on the rotation number set in the circulation number setting section. In an induction motor rotation speed control device that consists of a control circuit that gradually changes the voltage and frequency of the power supply and sets them to a predetermined value, overcurrent detects whether the current flowing through the induction motor via the inverter exceeds the allowable current. a detection circuit; an overvoltage detection circuit that detects whether the regenerative voltage from the induction motor is higher than an allowable voltage;
Since it is equipped with a stall prevention circuit formed by a date circuit that controls changes in voltage and frequency in the control circuit using the rain detection circuit output, the startup time will not be too long even if the load is not constant. This has the effect of preventing overvoltage and overcurrent trips from occurring and preventing stalls.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional example. 1 is an AC power supply, 2 is a converter, 3 is a voltage regulator, 4 is an inverter, 5 is a control circuit, 6 is an overcurrent detection circuit, 7 is an overvoltage detection circuit, 8 is an induction motor, and 9 is a stall prevention circuit. Agent Patent Attorney Ishi 1) Ai Shichi

Claims (1)

[Claims] (1) A converter that rectifies AC power and outputs DC power, a voltage regulator that chops the DC power output from the converter and makes the DC power voltage variable, and the voltage regulator output is input and induces the appropriate frequency. The inverter generates AC power to drive the motor, and the voltage regulator and inverter are controlled based on the rotation speed value set in the rotation speed setting section to gradually change the voltage and frequency of the AC power output from the inverter. In an induction motor rotation speed control device that includes a control circuit that sets a predetermined value using an overvoltage detection circuit that detects whether the voltage is higher than the allowable voltage; and a date circuit that controls voltage and frequency changes in the control circuit using the rain detection circuit output. Electric motor rotation speed control device.