JPH03159591A - Controller for motor - Google Patents

Abstract

PURPOSE:To prevent a transient overcurrent by applying phase control input of a thyristor power converter from another function generator during control insensitive zone period until a current control is established at the time of starting a motor to control to predict a motor current. CONSTITUTION:A set value of a function generator 6 normally becomes a rated current value of a motor, and the output of a phase control AMP 4 becomes a value capable of generating an output voltage necessary to supply a rate current at the time of stop of the motor. The output of the generator 6 supplies a starting current of a rated value or lower to the motor input to a power AMP 3 through a switching contact 5a, and an input from a current control AMP 2 during no control period until a current detector detects a current feedback C-FB is interrupted by a switching contact 5b. Thus, the motor can be started stably by a current near a rated value without transient overcurrent.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a control device for a motor using a thyristor power converter, and particularly relates to a circuit for suppressing excessive current when starting a motor. .

(Conventional technology) FIG. 5 shows a general configuration of a speed control device for an electric motor.

Further, FIG. 3 shows the conventional configuration of the control unit 12 in FIG. 5, and FIG. 4 is a time chart of voltages and currents at various parts during startup in FIG. In FIG. 5, 10 is a thyristor power converter connected in antiparallel, l2 is a control unit, 13 is a speed detector, l
4 is a current detector. In FIG. 3, 1 is a speed control AMP, 2 is a current control AMP, and 3 is a power AMP. 4 is a phase control AMP.

In FIG. 5, the armature current of the motor 11 is expressed as Ia. If the back electromotive force is E and the output voltage of the thyristor power converter 10 is V, then V = E + I1R + L - dIa/dt -
The relationship Q) holds true. Here, R is the main circuit resistance including the motor, and L is the main circuit inductance including the motor.

During operation at constant current, dIa/dt=O, so the output voltage V of the thyristor power converter 10 is V=E+I.
R...■R=Ra+RL
...(3). Here, Ra is the motor armature resistance, and R is the line resistance of the main circuit. When the operation command is turned on, the output of the speed control AMPI is clamped to the value CL corresponding to the current limit value, as shown in the time chart of Fig. 4, and the output of the current control AMP2 is also clamped to the AMP output limit value AL. Ru.

In this case, the rate of increase in the output voltage differs depending on the gain of the control system, and when the gain is high, it does not take the form of a first-order lag, so the output of the phase control AMP4 becomes the maximum value, and the output voltage of the thyristor power converter 10 V is close to the rated value. When the motor is stopped, the back electromotive force E=O, and the armature current ■8 at this time is calculated from the ω formula as Ia''(V L dI/dt)/R...
It is given as (4).

In general, V ) > L-dl/dt, and the value of R is also small, so (8) in equation O) results in a transient large current.

When current begins to flow, current detection operates and current control A
MP2 enters the control state and narrows down the phase of the phase control AMP4, thereby controlling the armature current (1)8 to the current limit value.

When the motor starts rotating and approaches the set speed, speed control A
MPI starts control and enters stable speed control.

(Problems to be Solved by the Invention) However, the conventional control circuit described above has the following problems.

(υ There is a control dead zone period from when the motor current is detected until the current control system starts operating, and the current during this period is (4
), resulting in an excessive current several times the motor rated current.

This control dead band period T is the sum of the delay T, = L/R due to the resistance R and inductance L of the main circuit of the motor, and the detection delay T2, T1 + T, and the period obtained by adding the detection current rise delay time to this value. is the uncontrolled period.

(2) The larger L of the motor main circuit, the smaller the current value in the control dead band, but the longer the non-control period.

(3) During the non-control period immediately after starting the electric motor, the electric 8! There is a risk of causing a current that exceeds the allowable current rise value of 200 to 400 PυPS (depending on the model).

As mentioned above, in conventional control methods, there is a control dead zone immediately after startup, which causes a rise in current that exceeds the motor's rated current or exceeds the allowable value. Therefore, frequent startups can cause motor brush burnout or flash flashes. The present invention was made in consideration of the above problems, and it establishes current control when starting the motor. It is an object of the present invention to provide a rational motor control device that prevents transient overload current by predictively controlling the motor current during the uncontrolled period.

[Structure of the invention]

(Means and effects for solving the problem) The present invention provides speed control AMP, current control AMP, and phase control AMP.
In a motor control device with a current minor loop that controls the speed of the motor by controlling the phase of a thyristor power converter for driving the motor, a control input for the starting current is given to the phase control AMP at the time of starting the motor. When starting the function generating circuit and the motor, the output of the function generating circuit is initially input to the phase control AMP, and when the detected current value for the current control AMP exceeds the set current value of the function generating circuit, A signal changeover switch is provided for inputting the output of the current control AMP to the phase control AMP,
This prevents transient excessive current during the uncontrolled period at startup, and enables stable startup.

(Example) An example of the present invention is shown in Fig. 1. Moreover, FIG. 2 is a time chart showing the operation.

In FIG. 1, 6 is a function generation circuit for predictive control;
(5a, 5b) are signal changeover switches for switching between the output of the current control AMP2 and the output of the function generation circuit 6 and inputting the same to the power amplifier AMP3; the other components are the same as in the conventional FIG. 3.

As shown in the time chart in Figure 2, when the motor operation command is turned on, the speed control AMPI is output at the current limit value C.
The output of the current control AMP2 is clamped to the AMP output limit value AL.

At startup, the signal changeover switch 5 selects the output side 5a of the function generation circuit 6. The selection conditions in this case are: (1) the operation signal is on; (2) the current detection value CF. B. is less than or equal to the current setting value of the function generation circuit 6, and (
3) The motor speed is zero.

The set value of the function generation circuit 6 is normally the rated current value of the motor, and the output of the phase control AMP 4 is set to the thyristor to generate the output voltage necessary for the rated current to flow when the motor is stopped. This is a value that can be generated by a power converter.

The output of the function generation circuit 6 passes through the switching contact 5a to the power AM
P3 causes a starting current below the rated value to flow through the motor, and the input from the current control AMP2 is cut off by the switching contact 5b during the non-control period until the current detection circuit detects the current feedback C-FB. Therefore, the motor can be stably started with a current near the rated current without generating a transient overcurrent.

FIG. 6 shows the relationship between the output of the phase control AMP 4 and the output of the thyristor power converter 10. The motor current rises and motor current feedback C-F. B. exceeds the current setting value of the function generation circuit 6, the signal changeover switch 5 closes the contact 5a.
is switched to the contact 5b side, the output of the current control AMP2 is input to the power AMP3, and normal speed control is performed and operation is performed.

〔Effect of the invention〕

As explained above, according to the present invention, the input for phase control of the thyristor power converter is given from another function generating circuit during the control dead zone period at the time of starting the motor, so that excessive current during transients at the time of starting is provided. By suppressing and stably shifting to the speed control circuit, it is possible to reduce the overload capacity of the motor and improve its life, and also to prevent element deterioration and reduce the withstand voltage of the thyristor power converter.

Fig. 2 is a time chart of signals of each part showing the operation of Fig. 2, Fig. 3 is a circuit configuration diagram showing an example of a conventional motor speed control device, Fig. 4 is a time chart showing the operation of Fig. 3,
Figure 5 is a general circuit diagram of a motor speed control device using a thyristor power converter, and Figure 6 is a diagram of a phase control AMP.
FIG. 3 is a characteristic diagram showing the relationship between the output of the thyristor power converter and the output of the thyristor power converter. 1...Speed control AMP 2...Current control A
MP3...Bawa AMP 4...Phase control AMP5...Signal changeover switch 6...Function generation circuit 10...Thyristor power converter 11...
Electric motor l2...Control unit 13...Speed detector l4...Current detector (8733)

Claims (1)

[Claims] Speed control AMP, current control AMP and phase control AMP
In a motor control device with a current minor loop that controls the speed of the motor by controlling the phase of a thyristor power converter for driving the motor, a control input for the starting current is given to the phase control AMP at the time of starting the motor. A function generation circuit, at the time of starting the motor, the output of the function generation circuit is initially input to the phase control AMP, and when the detected current value for the current control AMP exceeds the set current value of the function generation circuit, the output of the function generation circuit is input to the phase control AMP. A control device for an electric motor, comprising a signal changeover switch that inputs the output of the control AMP to the phase control AMP.