JPH04509A - Firing angle control device for thyristor converter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is particularly applicable to thyristor converters used in, for example, DC single-flow furnaces, which have a characteristic that there is a large time delay in the rise of a controlled variable during startup. This invention relates to a firing angle control device.

[Prior Art] FIG. 2 is a schematic diagram showing a DC arc furnace and its power supply device. In this diagram, a three-phase AC power source l as a commercial power source is shown.
The power supplied from the thyristor rectifier 2 is stepped down and rectified to obtain DC power, and this DC power is supplied to the DC arc furnace 3 via the DC circuit 21. The DC arc furnace 3 regenerates the iron scraps by passing a current through the iron scraps 32 through the electrodes 31 and heating and melting them.The voltage of the DC circuit 21 is as low as several hundred volts, but the current is 100K.
It is a large current of about A. The ignition angle of the thyristor rectifier 2 is controlled by the ignition pulse generated by the pulse generator 6, thereby controlling the arc current to be kept constant by quickly changing the DC voltage. In addition, the DC arc furnace 3 removes iron scraps 32 by moving the electrodes 31 up and down.
Alternatively, control is also performed to maintain the gap between this and the molten iron at an appropriate value.

The firing angle is controlled by the pulse generator 6 as follows. 19 on the leftmost side of the figure is a current setting value, and the control deviation as the difference between this setting value 10 and the current value i measured by the DC current transformer 7 provided in the DC circuit 21 is calculated by the subtractor 4. This control deviation is determined by the current regulator (AC
R) is input to the proportional-integral regulator 5 and a firing angle based on the output signal of the proportional-integral regulator 5 is generated by the pulse generator 6. There is a relationship in which the larger the firing angle α is, the lower the output voltage of the thyristor rectifier 2 is, and the roll-call angle α is the minimum α. , 9, the output voltage of the thyristor rectifier 2 becomes the highest voltage (2) of 1.8, and when the firing angle α is the maximum α, 18, the output voltage of the thyristor rectifier 2 becomes the lowest voltage (2), , 7. The initial value for starting the device is set to the maximum firing angle α1.8 at which the output voltage is the lowest. The actual current value i can be obtained by rectifying the three-phase current on the alternating current side of the thyristor rectifier 2 via a current transformer, in addition to being obtained by the DC current transformer 7 as shown.

FIG. 3 is a circuit diagram showing the configuration of the proportional-integral regulator 5 and subtractor 4 of FIG. 2. In this figure, the proportional-integral regulator 50 is replaced by an operational amplifier 51 used as an inverting amplifier.
By connecting a series circuit of a resistor 54 and a capacitor 55 to the output side and the input side to perform feedback, a proportional-integral regulator in which a proportional element and an integral element are connected in parallel can be equivalently created. The configuration has been realized.

At the same time, the input signal of the operational amplifier 51 is inputted from the terminal 56 via the resistor 52 to the current setting value 10 and the terminal 57
and -1, which is an inverted signal of the measured current value i inputted through the resistor 53, and this configuration is a subtracter using the operational amplifier 51. Although the subtracter 4 and the proportional-integral regulator 5 are shown as separate units in FIG. 2, the circuit shown in FIG. 3 has them in a mixed form. However, there are various types of circuits constituting the proportional-integral regulator 5 and the subtracter 4, and the circuits are not limited to the configuration shown in FIG.

[Problem to be solved by the invention]

When starting these devices, the thyristor rectifier 2 is connected to the AC power source 1 using a switch (not shown), and the electrode 31, which was initially at the highest position, is lowered downward to generate an arc. The direct current is controlled to a predetermined value by controlling the upper and lower positions of 31 and the firing angle.

During the process of lowering the electrode 31 after startup, arcing is still occurring, so the current i measured by the DC current transformer 7
is zero. For this reason, the control deviation as the input signal of the proportional-integral regulator 5 becomes the current setting value i''' itself, and a positive value is always manually input, so the output signal of the proportional-integral regulator 5 is integrated. As a result of the element including a value obtained by time-integrating the current setting value 10, the value increases as time passes after startup, and accordingly, the firing angle α of the pulse emitted by the pulse generator 6 changes from the initial value α1. It decreases over time from .8 and stops only when it reaches α11.As a result, the output voltage of the thyristor rectifier 2, which was the lowest voltage V sin immediately after starting, becomes so high that an arc occurs. The highest voltage V before the electrode 31 drops
111111, and when a current starts to flow after that, a problem arises in that an excessive current flows. Since the change in the vertical position of the electric current 8i31 is much slower than the current control using the firing angle α, the firing angle control is activated as described above before the electric current 131 has completely fallen. Problems arise;
As a result, there is a problem that normal startup becomes difficult.

An object of the present invention is to solve such problems and provide a firing angle control device for a thyristor converter that enables normal startup by suppressing a decrease in the firing angle α at startup. .

[Means to solve the problem]

In order to solve the above problems, according to the present invention, a proportional-integral regulator is provided which takes as an input signal a control deviation obtained by subtracting a control amount from a set value, and the point of the thyristor element is adjusted based on the output signal of the proportional-integral regulator. In a firing angle control device for a thyristor converter in which an arc angle is set, negative feedback is provided to the proportional integral TSM device via a proportional element, and the proportional element is controlled by a zero hold circuit according to the value of the controlled variable. The zero hold circuit applies zero hold when the controlled amount is zero or smaller than a predetermined value, and releases the zero hold at other times.

[Effect]

In the configuration of this invention, by applying negative feedback to the proportional-integral regulator via the proportional element, the larger the proportional coefficient of this proportional element, the smaller the influence of the integral element of the proportional-integral tIgs regulator, and the proportional coefficient becomes sufficiently large. Sometimes it has the property of being a mere proportional regulator. A zero hold circuit is provided in the proportional element for this feedback, and control is performed such that zero hold is canceled when the controlled amount is zero or small, and zero hold is applied when the controlled amount is equal to or greater than a predetermined value. When the controlled variable is zero or a small value when the device is started, zero hold is applied and the aforementioned feedbank becomes effective, reducing the influence of the integral element of the proportional-integral regulator. It is possible to suppress an increase in the output signal of the regulator. When the controlled variable reaches a predetermined value after a period of time has elapsed after startup, the zero hold is released, so that the proportional-integral regulator operates normally and the controlled variable is controlled as before. Therefore, if the controlled variable remains zero after startup or has a slow rise characteristic, the value of the control deviation, which is the difference between the set value, which is the input signal of the proportional-integral regulator, and the controlled variable will always be It is possible to avoid the problem that the output signal increases due to the positive value.

〔Example〕

The present invention will be explained below based on examples. FIG. 1 is a circuit showing a main part of an embodiment of the present invention.

The firing angle control device shown in FIG. 1 mainly includes a proportional integral 50, a first proportional element 60, and a second proportional element 70.
and a zero hold circuit 80. The proportional-integral regulator 50 and the resistor 5253 on the input side thereof are connected to the second
It is the same as the figure, and detailed explanation will be omitted. A first proportional element 60 is connected in series to the output side of the proportional-integral regulator 50, and a second proportional element 70 is connected from the output side of the first proportional element 60 to the input side of the proportional-integral regulator 50. The structure is designed to provide feedback. A zero hold circuit 80 is connected to the second proportional element 70 and can hold or release the output signal of the second proportional element 70 to zero. This zero hold control is performed depending on whether or not the measured current i is zero, as will be described later.

The first proportional element 60 employs a proportional element configuration in which an operational amplifier 61 is fed back through a resistor 63.
Like the proportional-integral regulator 50, it is connected as an inverting amplifier. The proportional coefficient as the amplification factor of the first proportional element 60 is determined by the ratio of the resistance values of the resistors 62 and 63.

The second proportional element 70 also basically has the same configuration as the first proportional element 60, but a zero hold circuit 80 is connected to its output side. This zero hold circuit 80 is driven by the switching element 81 driven by the current i as described above, and when the current i is zero, the switching element 81 is turned off, and as a result, the zero hold by the zero hold circuit is It is in the released state, and when the current i is no longer zero, zero hold is applied and the influence of feedback via the second proportional element 70 is eliminated.

When the current i is zero and the zero hold is released, feedback via the first proportional element 60 and the second proportional element 70 works to reduce the influence of the integral element of the proportional integral regulator 50. The degree is 1 to the proportional coefficient of the first proportional element 60.
and the proportional coefficient of the second proportional element 70 change depending on the value of 2, so these two coefficients can be optimally selected.

Now, assume that the power is turned on to start the DC arc furnace 3. As mentioned above, there is a time delay before the electrode 31 descends and an arc is generated. During this time, the current i is zero, so the zero hold circuit 80 is in the state where the zero hold is released as described above, and the feedback by the second proportional element 70 is working effectively, and the influence of the integral element of the proportional integral regulator 50 is suppressed.

The transfer function of the proportional-integral regulator 50 is expressed as follows. however,
S is the Laplace transform operator, K is the proportionality coefficient of the proportional element,
T is the time constant of the integral element.

l Fo (s) −K+− The transfer function in FIG. 1 in a state where zero hold is released is as follows.

If the second term is so large that 1 in the first term of the denominator can be ignored, the value of F(s) will be 17 to 2, making it a mere proportional element, and the influence of the integral element will disappear, and the proportional element will also be The proportional coefficient K is 1/! It becomes J.

Furthermore, when zero hold is applied, the value of F(s) is 2-0, so the value of F(s) matches Fo(s) in equation (1). By appropriately selecting the value of K2, it is possible to obtain a transfer function in which the integral element is appropriately suppressed.

In the device having the configuration shown in FIG. 2, it is better not to have an integral element at startup, so it is appropriate to set the proportionality coefficient to a sufficiently large value of 8. In this case, as mentioned above, the circuit in Fig. 1 essentially becomes a proportional element and its proportional coefficient also becomes a small value, so its output signal becomes a small value proportional to the current setting value i° and increases over time. Therefore, the state in which the firing angle α is initially set to the maximum firing angle αw+*x is maintained as it is, and after the point when the current i is no longer zero, this current i Normal control is performed so that the set value becomes 1''.

The insertion position of the first proportional element 60 in FIG. 1 may not be on the output side of the proportional-integral regulator 50 as shown in the figure, but may be inserted in series in the feedback circuit like the second proportional element, or , the first and second proportional elements 6 as described above.
0.70 are both configured as inverting amplifiers, but instead of this, a configuration may be adopted in which the proportional element 70 is configured as a non-inverting amplifier and the first proportional element is omitted.

In the configuration shown in FIG. 1, the output signal is inverted by the first proportional element 60, so the pulse generator that uses this output signal as an input signal has a phase difference of the input signal with respect to the pulse generator 6 shown in FIG. However, if the first proportional element 60 is omitted and the second proportional element 70 is configured as a non-inverting amplification, such a difference will not occur.

The zero hold circuit 80 in FIG. 1 has a configuration in which a zero hold circuit 82 is inserted in series on the output side of the second proportional element 70, but the proportional element 70 using an operational amplifier
In addition to this configuration, there is also a configuration in which zero hold is applied, for example, by short-circuiting the feedback resistor 73 with a switching element, and the configuration of the zero hold circuit is not limited to the configuration shown in FIG.

In the above-mentioned embodiment, the load was a DC arc furnace, and the purpose was to solve the control problem caused by the delay in the rise of the current due to the delay in the descent of the electrode after startup. The present invention is not limited to the case where the load is a DC arc furnace. For example, the present invention can be effectively applied to a speed control device for an electric motor that drives a load that has a large inertia at the time of startup and whose rotational speed rises slowly. In such a case, a configuration is adopted in which the speed of the motor is measured instead of the current in the above embodiment, and the integral element of the proportional-integral regulator is suppressed until the measured value reaches a predetermined value. Become.

[Effects of the Invention] As described above, this invention has the characteristic that when negative feedback is applied to a proportional integral meter through a proportional element, when the proportional coefficient of this proportional element is sufficiently large, it becomes a mere proportional regulator. It will be done. A zero hold circuit is provided in this proportional element to release zero hold when the controlled amount is zero or small, and apply zero hold when it exceeds a predetermined value.

When the controlled variable at startup of the device is zero or a small value, zero hold is applied and the aforementioned feedback becomes effective, reducing the influence of the integral element of the proportional-integral regulator and reducing the proportional coefficient of the proportional element to a small value. Therefore, since the output signal of the proportional-integral regulator due to the delay in the rise of the controlled variable can be maintained at a small value, the value of the firing angle α is maintained at its initial value. When the controlled variable reaches a predetermined value after a period of time has elapsed after startup, the zero hold is released, and the proportional-integral regulator operates normally, so that conventional control over the controlled variable is performed. Therefore, the control amount may remain zero after startup, or it may have a slow start-up characteristic.
The advantageous effect is that the thyristor rectifier can perform good startup even for loads with poor response during startup.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the main parts of an embodiment of the present invention, FIG. 2 is a schematic diagram showing a DC arc furnace and its power supply device, and FIG. 3 is a schematic diagram showing a direct current arc furnace and its power supply device. FIG. 2 is a circuit diagram showing the configuration. 52, 53. 54. 62. 63. 7255・
... Capacitor, 81... Switch 82... Zero hold circuit. 73, 74...Resistor, switching element, 1...AC power supply, 2...Thyristor rectifier (thyristor converter), 21
...DC circuit, 3...DC arc furnace, 4...Subtractor, 5.50...Proportional integral regulator, 6...Pulse generator, 7...DC current transformer, 60 .70... Proportional element, 80... Zero hold circuit, 51.61.71.
...Operation amplifier, Figure 2, upper part, Ronerud Group, Figure 1, Figure 3?21

Claims (1)

[Claims] 1) A proportional-integral regulator whose input signal is a control deviation obtained by subtracting a control amount from a set value, and a firing angle of a thyristor element is set based on an output signal of the proportional-integral regulator. In the firing angle control device for a thyristor converter, the proportional-integral regulator is provided with negative feedback via a proportional element, the proportional element is provided with a zero hold circuit controlled by the value of the control amount, and the control A firing angle control device for a thyristor converter, characterized in that the zero hold circuit applies zero hold when the amount is zero or smaller than a predetermined value, and releases the zero hold at other times.