SU418952A1 - DEVICE FOR CONTROLLING THE CONVERTER ^ ^ ^ ^ '-' 't; ./' FREQUENCIES - Google Patents

Description

The invention relates to a converter technique, in particular to a frequency conversion technique for induction heating.

Devices are known that contain an inverter output voltage measuring transformer, a comparator unit and a control pulse generator that stabilize one of the output parameters (for example, the voltage at the load terminals) by changing the frequency of the control pulses if the converter inverter has independent excitation, or by changing the phase angle between the output voltage and the output current, if the inverter is operating in self-excitation mode. When powering several induction posts, the disconnection of one of the posts leads to a change in the total load of the converter. The known devices at the same time keep the output voltage constant by varying the frequency. With variations in the voltage of the power network, the frequency of the output voltage also changes. Since the power consumed by the induction installation depends not only on the voltage applied to it, but also on the frequency, the use of known devices does not ensure the stabilization of the heating mode in each induction post separately.

In order to eliminate these drawbacks, the proposed device is equipped with a functional converter, the output voltage of which is directly proportional to the effective value of the input voltage and inversely proportional to the power function of the frequency, the input of the functional converter being connected to the measuring transformer and the output to the comparison node.

FIG. 1 shows a block diagram of the proposed device; in fig. 2 and 3 are embodiments.

Inverter 1 is controlled by a pulse generator 2. To the output of inverter 1, a voltage measuring transformer 3 is connected, the output of which is connected via a functional converter 4 to a comparison node 5, to the input of which a reference voltage is applied

t / on.

The device works as follows. The output voltage U of the inverter 1 through the voltage transformer 3 is fed to the input of the functional converter 4, the output of which forms the signal C / f, equal to

and

u k (1)

0.5

where K is a constant coefficient;

n - the exponent lying in the range of 0.5-1.5.

Comparison node 5 provides a comparison of the voltages f / f and Uon and provides an error signal to the input of the generator 2. The closed frequency control system supports the equality / f | SOF31.

Since the equivalent resistance of an inductive installation depends on the frequency

D- D I

A - AO -

base frequency; 10

the equivalent resistance at the base frequency, and the power consumed by one induction post, is determined by the expression:

P- ± i

R RO K

It is obvious that the device provides a constant power consumed by each of the heating posts, regardless of voltage fluctuations in the network and the number of posts connected to the frequency converter.

FIG. 2 shows the first embodiment of the functional converter 4.

The choke 6 is connected in series with the bridge rectifier 7, loaded on the resistor 8. The output voltage of this circuit with an accuracy of 0.2% approximates expression (1) when the frequency is changed by 40%.

FIG. 3 shows a second embodiment of the functional converter 4. The voltage from the sensor 3 is supplied to a series circuit consisting of a resistor 9 and a parallel connected capacitor 10 and

bridge rectifier 7, loaded on the resistor 8. The output voltage of this circuit also well approximates the expression (1).

Subject invention

Claims (3)

1. A device for controlling a frequency converter of induction heating installations, comprising a pulse generator for controlling an inverter converter, a measuring transformer of an output voltage of an inverter, and a comparison unit, characterized in that, in order to reduce the influence of the number of connected installations and fluctuations of the network voltage heating mode, it is equipped with a functional converter, the output voltage of which is directly proportional to the actual value of the input voltage and inversely proportional to but exponential function of frequency, the input function generator connected to the measuring transformer, and the output - to the comparison node. 2. The device according to claim 1, characterized in that, in order to simplify the device, the functional converter is made in the form of a chain of series-connected inductance element and a bridge rectifier loaded on a resistor. 3. The device according to claim 1, characterized in that the functional converter is made in the form of a series circuit of a resistor and a parallel-connected capacitor and a bridge rectifier, loaded on another resistor. V. on  node 5 N knots /} y5