SU811488A1 - Method of control of frequency converter with direct coupling and artificial switching - Google Patents

Description

the holders are set according to the nominal load of the inverter, then when the loads are less than the nominal load, the commutation chokes of the power thyristor bridges will be shorted.

The aim of the invention is to increase the reliability of the artificial switching node.

This goal is achieved by the fact that, according to the method of controlling the frequency converter with direct connection and artificial switching, they contain, they and power thyristor bridges, shunted by switching throttles, and a common artificial switching node connected via distribution gates to the terminals of the power bridges, The instantaneous values of the phases of the load and the recharge current of the switching capacitors of the artificial switching node are measured, the currents of the phases of the load are rectified, the signal is compared, oportsionalny rectified load current with a signal proportional to the current commutating capacitor overcharge and when they are equal produces a pulse on the power switch for closing thyristor converter terminals.

FIG. Figure 1 shows a simplified diagram of a frequency converter, explaining the proposed. My control method for a three-phase network; in fig. 2 - diagrams of control pulses of the IF data.

The frequency converter contains power thyristor bridges 1–3, triggered by switching glands 4–6, a common node / artificial switching, connected through distribution valves 8–13 to the DC terminals of power bridges. In addition, it contains sensors 14-16 of the instantaneous value of the load phase currents, connected to the inputs of the auxiliary rectifier 17, the output of which is connected to the comparison unit 18, to the other input of which the output of the sensor 19 of the instantaneous value of the recharging current of switching capacitors is connected. 14, the output of the comparator unit is connected to the control system 20 of the inverter, which controls the thyristors of the power bridges of the converter.

The timing diagram shows the instantaneous current values of 21 Artificial Switching Nodes; load current 22 at rectifier output 17; voltage 23 at the output of the comparison block 18; voltage 24 at the output of the control system 20; pulses 25 to turn on the power thyristors for closing the output terminals of the converter; impulses 26 pa switching on power thyristors.

The Converter operates as follows. Suppose that at the moment of time tQ it is necessary to switch off the current thyristors of the power bridges 1-3 of the converter, and the inverter load is actively inductive in nature. For this, all thyristors of power bridges 1-3 are applied through distribution diodes 8-13

negative voltage of commuting capacitors of the common node 7 of artificial switching. The conducting thyristors are turned off, and necessary to restore the thyristor locking properties

the time is ensured by the flow of current recharging the switching capacitors of the node 7 through distribution diodes 8-13 and chokes 4-6. The reactive load current then closes through

node 7 artificial switching, recharging commuting capacitors. The signals from the i4-16 sensors are proportional to the instantaneous values of the phase load currents and rectified by the auxiliary

The rectifier 17 is fed to the input of the comparison unit 18, to the other input of which a signal 21 is supplied from the sensor 19 of the instantaneous value of the recharge current of the switching capacitors. Duration of the signal

23 at the output of block 18 depends on the value of the load current of the inverter and is determined by the moment of equality of the currents of the recharging of the switching capacitors and the load (moment i). Signal 23 from block 18 output

enters the control system 20 of the inverter, where a signal 25 is generated at its falling edge to turn on the power thyristors, which close the output terminals of the converter. After working out the pause,

required for BW, the indicated thyristors are turned off by node 7, and the control system generates pulses 26 to turn on the next power thyristors of the bridges.

For comparison, in FIG. 2 shows sigpals 24 shifted by 120 al. hail., control pulses of the power thyristors of bridges 114 in the absence of delay, as well as a pause in SHIR.

Beginning at time / 3, processes similar to those described above are repeated. For other load currents, the delay value will automatically change. 1In this way, according to this control method, the delay time for switching on the thyristors that close the output terminals of the converter is not fixed and varies at different switching intervals depending on the magnitude of the reactive load current.

With this method of control, the losses in the artificial switching node decrease, and the efficiency of the converter increases.

and the installed power of the power elements of the IF circuit (switching capacitors, chokes, distribution diodes) is reduced, and the class of thyristors used is reduced, which increases the reliability of the converter.

Claims (2)

1. USSR author's certificate number 477505, cl. H 02 P 5/28, 1973. 2. USSR author's certificate number 483746, cl. H 02R 5/28, 1973 (prototype). 2J ts