SU1661942A1 - Direct frequency converter - Google Patents

Abstract

The invention relates to power converter technology. The goal is to increase the frequency range of the output voltage. The converter contains a bridge of main thyristors 1-6, controlled by means of distribution thyristors 7, 8 through diodes 11-16, half-windings 9, 10 of the reactor connected at the output of this bridge, and capacitors 17-19 connected between the input terminals A, B c the converter and the midpoint of the reactor winding, which is one output terminal of the converter. The second output terminal of the converter is the zero point of the supply network. The control unit contains two frequency controlors and two two-input logic element 2 AND the coincidence of the outputs associated with the control inputs of the distribution thyristors. 3 il.

Description

one

(21) 4625567/07 (22) 12.26.88 (46) 07.07.91. Bul No. 25

(71) Leningrad Institute of Water Transport

(72) C. F. Semoseyko and N. V. Belousova (53) 621.314.27t088.8)

(56) Kartashov R.P., Kulish A.K. and Chekhet E.M. Thyristor frequency converters with

artificial switching. - Kiev: Technique, 1979, p. 150

Electrical products and devices. Electrotechnical Handbook, V. 2. - M: Energoatomizdat, 1986, p. 63, fig. 32.30. (54) DIRECT FREQUENCY CONVERTER

(57) The invention relates to power converter technology. Target - Increase20 UQ

range span adjustment of output voltage frequency. The converter contains a bridge of main thyristors 1-6, controlled by means of distribution thyristors 7 and 8 through diodes 11-16, half-windings 9 and 10 of the reactor connected at the output of this bridge, and capacitors 17-19 connected between inputs A, B the converter and the midpoint of the reactor winding, which is one output terminal of the converter. The second output terminal of the converter is the zero point of the supply network. The control unit contains two frequency adjusters and two two-input logic elements 2 and 1 coincident with the outputs associated with the control inputs of the distribution thyristors. 3 il.

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The invention relates to electrical engineering and can be used as a converter for three-phase alternating voltage of one frequency into single-phase alternating voltage of another frequency.

The purpose of the invention is to expand the functionality by expanding the range of output voltage frequency control.

FIG. 1 is a diagram of a direct frequency converter; in fig.

2 is a diagram of a direct frequency converter control system; in fig.

3a-d are diagrams of impulses of the frequency adjuster fo, paraphase impulses fi and f2, the three-phase system of phase emf U, e, its, output voltage U0, and voltage UA, UB, Uc on the capacitors, respectively.

The direct frequency converter contains thyristors 1-8, half windings of 9 and 10 mid-point reactors, diodes 11-16, capacitors 17-19, forming a star connected by phase leads to the phase leads of the bridge formed by thyristor 1-6, the DC outputs of which connected to the semi-windings 9 and 10 of the reactor, the midpoint of which is connected to the zero point of the star capacitors 17-19 and the first output of load 20, the second output of which is connected to the zero point of the three-phase voltage system. Diodes 11-13. form a cathode group connected by phase leads to a three-phase voltage system, and cathodes to an anode of thyristor 7, the anode of which is connected to control electrodes of thyristors 1, 3 and 5, Diodes 14-16 form an anode group connected by phase leads to thyristor control electrodes 4, 6 and 2, and anodes - to the cathode of the thyristor 8, the anode of which is connected to the anodes of the anode group formed by thyristors 2, 4 and 6.

The control unit consists of a setpoint generator 21 of the output frequency with paraphase outputs and a setpoint generator 22 of higher frequency, two two-input elements 2I 23 and 24, connected with the first inputs respectively with the paraphase outputs of the setpoint 21 frequency, the second inputs with the output of the setpoint 22, and outputs with inputs respectively thyristors 7 and 8.

The direct frequency converter works as follows.

Control pulses from the control unit (and feu where fi, fa are paraphase frequency setting pulses 17 having a period Ti; f0 are frequency setting pulses 18 having a period T0) are sent to thyristors 7 and 8.

The period of the three-phase system of voltages T and the periods T0 and Ti are generally non-multiple.

In the absence of pulses, FI and F2, the voltage on capacitors 17-19, which have the same capacitance, is equal to the emf, u, it. The voltage between the star zero of the capacitors 17-19 and the zero of the three-phase voltage system is in this case zero.

0 Suppose that at the time of arrival of the clock pulse f0, and the EMF unit is maximum (Fig. 3). In this case, the thyristor 7 is opened, and a current flows through the circuit of elements 11-7-1-9, which leads to the unlocking of the thyristor 1, after which the thyristor 7 is shunted and as a result closes. Thyristor 1, inductance 9 and capacitor 17 form an oscillating circuit, the opposite half-wave current

0 which closes the thyristor 1 and recharges the capacitor 17 so that it has a negative voltage.

If the inductance 9 is small, then the period of natural oscillations of the circuit will also be small. Accordingly, the duration of the open state of the thyristor 1, equal to the half-period of natural oscillations, will be small.

Since the load voltage is 20

0 U0 eA-UA and taking into account that, and after recharging the capacitor 17 is negative, the voltage across the load will be positive. After the thyristor 1 is locked, the capacitors 17-19 begin to recharge.

5 in such a way that the voltage on them will tend to emf u, its L

After the arrival of the next FI pulse, all processes are repeated. In this case, each time the thyristor is turned on, at which the maximum positive voltage will be at a given moment in time. As a result, a series of voltage pulses of positive polarity is generated on the load.

5 In the case of the arrival of the pulse F2 at tyri-4

line 8 processes proceed as follows. Suppose that at the moment of arrival of the pulse F2 to the thyristor 8 on the capacitor 17 there will be the lowest voltage. After

0 opening of the thyristor 8, a circuit is formed of elements 10-8-14-4, through which current flows, 0, as a result of which thyristor 4 opens, shunts thyristor 8, and the latter closes. In the resulting chain

5 elements 17-10-4 of the oscillatory circuit, a current flows, the reverse of the half-wave of which leads to the closing of the thyristor and the recharging of the capacitor 17, after which the last has a positive voltage. In this case, the voltage at the load U0 eA-UA О

After the thyristor is locked, capacitors 17–17 are recharged and the voltage across the load tends to zero. When the next pulse F2 arrives, all processes proceed in a similar way. In this case, the frequency of each thyristor 8 turn on includes that of thyristors 2, 4, and 6, where the lowest voltage will be applied. As a result, a series of negative-field impulses is formed on the load (Fig. 3g).

The alternation of pulses fi and f2 leads to alternation of a series of positive and negative voltage pulses on the load. As a result, the main period of the output voltage is equal to TL. It can be adjusted over a wide range. A limitation in the direction of decreasing Ti is the time for recharging the capacitors when unlocking the thyristors 1-60, which in turn is limited by the turning off time of the thyristors.

By modulating a sequence of pulses fo, one can achieve a voltage form that is closest to sinusoidal. The effective value of the voltage can be adjusted by changing the pulse frequency f0.

Thus, the proposed direct frequency converter allows you to adjust both the magnitude of the actual voltage on the load and its shape and has a wide frequency control range due to artificial switching of the thyristors. In addition, the converter has a fairly simple power structure. The thyristors in it are open for a short time and perform only the switching function. Consequently, their weight and size indicators will be small. The main load is carried by capacitors.

Claims (1)

Invention Formula A direct frequency converter containing a three-phase thyristor bridge, the phase terminals of which are its inputs connected to a three-phase voltage system with a zero point, and the DC terminals of the bridge are closed at a choke with a midpoint, which together with the specified point forms the zero output of the converter as well as a control unit that includes the first output frequency setting unit with a paraphase output and a second higher setting setting unit, characterized in that, in order to increase the control range output voltage frequencies, three capacitors are inserted in it, some plates of which are connected to the corresponding phase outputs of the bridge, and others to the midpoint of the mentioned chokes, three-phase anode group of diodes connected by cathodes to the control electrodes of the bridge anode group, three-phase cathode group diodes connected by phase leads to the phase leads of the bridge, and two thyristors, the anode of the first of which. The cathode is connected to the anodes of the anode group of diodes, the anode of the second thyristor is connected to the cathodes of the cathode group of diodes, the cathode to the control electrodes of the cathode group of the bridge; the two input two-input logic elements 21/1, the second inputs of which are connected to the output of the second frequency sensor, and the outputs of the elements 2I are connected respectively to the inputs of the first and second tiris tori. a l I I I I I I I I | I I I s I II I ll | I II In rSF g I I II -3B feJ