SU1181086A1 - Bridge thyristor frequency converter - Google Patents

Abstract

BRIDGE TIRISTOR FREQUENCY CONVERTER, containing a three-phase matching transformer with two secondary three-phase windings, six thyristor bridges. connected in pairs in series on the output and free DC outputs connected to a smoothing choke, common for three pairs of bridges, and the junction points of the bridges form the output transducers of the converter, characterized in that, in order to improve the mass and energy indicators, it is equipped with a third secondary three-phase winding, . with each of the three secondary three-phase windings connected to the inputs of the bridge thyristors. belonging to one pair. g

Description

00 Od 1 The invention relates to devices for converter equipment and, in particular, to power circuits of frequency converters with direct coupling, which form the load current in terms of magnitude and frequency by switching the load current with voltage. The aim of the invention is to improve the mass, energy and energy performance of the transducer by reducing the installed power of the transformer and improving the switching conditions of the thyristors. On (Jfer.l is a diagram of the proposed frequency converter; FIG. 2 is a block diagram of a frequency converter control system, which allows to realize the necessary law for the formation of the load current; and FIGS. 3 and 4 are diagrams explaining the formation principle output currents and the operation of the converter control system, respectively. The frequency converter (Fig. 1) contains a matching transformer 1, a smoothing choke 2, six bridge groups 3-8 and a load 9. Bridges 3-8 are connected in series two and form valve groups of three output phases Each pair of series-connected bridges is powered from a separate three-phase transformer or from a separate three-phase winding trap phase transformer 1 windings, and the bridge junction points are the output terminals of the converter to which the AC-load motor connects. 4, 5-6 and 7-8 are connected in parallel and a smoothing choke is connected between their common terminals. The frequency converter forms a load current, the shape of which, under conditions of ii high inductance choke 2 DC link shown in fig.Z. The duration of a half-wave current in the load phase is t rad. the output frequency, and in the areas of current switching between the phases of the load (the section corresponds to the duration of the rad; output frequency) three valve bridge groups participate in the work, and at other points of time - two valve groups 862 of the converter. The amplitude of the load current is determined by the thyristor control angle in groups о ((Fig.4) and the switching time is determined by the load parameters, current magnitude and phase value of the thyristor control angle in the inverter mode (Fig.4). Consider the process of generating the load current. At time t (Fig. 2), the control pulses go to the thyristors of bridges 3 and 8. The load current flows in a loop: the secondary windings of the transformer 1, the cathode group of gates of the bridge 3, phase A of the load, phase C of the load, the anodic group of gates of the bridge 8 Tue The transformer 1 windings, the cathode group of bridge valves 8, the choke 2, the anode group of bridge 3, the transformer windings 1. At time t, the control pulses are applied to the thyristors of bridge 5, and bridge 3 is switched to inverter mode. During switching time, the load current passes from phase Aj to phase B. ,, At the time of Time tj, the control pulses are removed from the bridge thyristors 3 and in operation bridges 5 and 8 remain. Next, the processes in the circuit are repeated with a period of:: g radians of the output frequency. Fig. 2, by way of example, shows a block diagram of a converter control system that implements the described principle of forming a load current. Since the frequency converter operates in current source mode, the external reference signal in the control system is the amplitude and frequency setting signal. The internal control devices are pulsed-phase control systems (CIFS) 10, current zero sensors 11 in load phases, logic circuit 12, allowing control pulses to flow to the thyristors of each bridge, as well as a controlled master oscillator 13, a scaling ring 14, a sensor 15 current in the circuit of the throttle and current regulator 16. These functional units of the converter control system can be performed by any known schemes. A feature of the control system is that the SIFU generates two sequences of pulses .; one with a variable control angle (oLy О + 150) determined by the control voltage, the other with a fixed angle of control (oi 150) of the limit inverter mode.

At the input of current regulator 16, the signals for setting the amplitude of the alternating current HFSSA signal of the current sensor 15 in the throttle circuit 2 are compared. The output signal of the current regulator is fed to the input of SIFU 10, at the output of SIFU receive two sequences of pulses with control angles and each It has six channels for the number of thyristors of a rectifying bridge.

Figure 4 shows pulses and oiy for one thyristor (I, period of mains frequency).

Ur frequency reference signal ..

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(LF) is fed to the input of a controlled master oscillator 13, pulses are received at its output, the frequency of which is proportional to these pulses control the operation of counting ring 14, the output of which receives six signals of duration Tj / 3 (Tj is the period of output frequency) corresponding to the reference operation of valve bridges 3-8 (figure 1). Figure 4 shows the signals for setting the operation of groups 3 and 5 are the signals and, respectively. The sensors 11 zero phase load currents (figure 2) give logical signals of the presence of the load current, for example for phase AJ (bridges 3 and 4)

1810864

this is the signal A 7-3.4 inverse signal A Y-3 4 (figure 4).

All the considered signals are fed to the inputs of the logic circuit 12, 5 which has 36 (by the number of thyristors) logic combinational circuits functioning similarly according to the following principle.,

For example, for one thyristor

10 of bridge 3 (figure 5) in the presence of the signal AJ, the output of the logic circuit receives pulses for a given thyristor with the oLy phase. When a signal appears, the AJJJ signal is removed, but

15, current through bridge 3 X continues to flow, for some time current 3 flows partially through bridge 3 and partially through bridge 5. At this time, corresponding to the logical combination of xA signals, y is fed to the considered thyristor pulses with phase C1 and -FIG.4 The control pulses for one thyristor of bridge 3 are shown below.

25 Thus, the control system provides the formation of output currents of a given frequency and amplitude, and a separate control of bridges related to one phase of the converter.

The invention eliminates the need to increase by 2 times the power supply voltage of the converter bridges to ensure the switching current conditions of the load when the back-EMF and load parameters change, which ultimately either widens the range of use over the output frequency, or even weight and energy parameters of the converter.

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Claims (1)

A BRIDGE thyristor frequency converter, comprising a three-phase matching transformer with two secondary three-phase windings, six thyristor bridges connected in pairs in series at the output and free DC leads connected to a common inductor for three pairs of bridges, and the connection points of the bridges form the output terminals of the converter that, in order to improve the overall dimensions and energy indicators, it is equipped with a third secondary three-phaen winding, 'each The third of the three three-phase secondary windings is connected to the inputs of the bridge thyristors belonging to one pair. . § ω > 1111