SU650202A1 - Method of control of single-phase power-diode frequency converter - Google Patents

Description

one

The invention relates to electrical engineering, in particular to methods of controlling valve converters, the output frequency of which is equal to the difference between the frequencies of the network and control loaded on reactors with a linear characteristic.

It can be used to develop means of improving the quality of electrical energy in single- and multiphase networks of stable or varying frequency with non-linear loads, in the current consumption curve of which there is a constant or low-frequency component (for example, thyristor power controllers with phase control, single-phase welding, arc furnaces, rectifiers for charging capacitive accumulators, electrical sources of asymmetric current, etc.).

Known methods of controlling frequency converter converters offer such control of valves in which the phase of the control pulses does not change with respect to the maximum of the supply voltage 1, 2.

Of the known control methods, the closest one: the technical essence is the control method of a single-phase gate converter, where

the valves are controlled with a frequency equal to the network frequency half 3.

A disadvantage of the known control method is that the control impulses are rigidly synchronized with the phase of the supply voltage. With this control method, the converter cannot generate a direct or low frequency component of the current, which is adjustable in magnitude and sign, to the network.

The aim of the invention is to compensate for the constant or low frequency component of the current consumed from the mains by a nonlinear load. In this case, the converter generates into the network a constant or low-frequency component of the current, equal in magnitude and opposite in sign to the current of the nonlinear load.

For this, in the known method of controlling a single-phase valve frequency converter loaded on a reactor with a linear characteristic, the control of which valves are produced with a frequency equal to half the network frequency, they additionally form a constant or low-frequency component of the current equal in magnitude and opposite in sign to the same the component in the current of the nonlinear load, and the phase of the control pulses of the valves is controlled from -45 el. hail, up to +45 el. hail, in relation to the maximum of the mains voltage.

FIG. Figure 1 shows a diagram of one of the embodiments of the proposed method of controlling a converter when the latter is used as a constant-current compensator consumed from a network with a single-phase non-linear load supplied from an alternator; FIG. 2 - the same, the load supplied from the transformer; FIG. 3- curves of currents and voltages in the power elements of the converter circuit; FIG. 4- dependence of the relative value of the constant component of the current on the initial phase of the control pulses of the converter valves.

FIG. 1, 2 marked: non-linear load 1, connected directly to the alternator 2, or through a matching transformer 3; single-phase valve frequency converter, made by transformer 4, or bridge 5 circuits, on valves with bilateral conductivity 6; linear reactor 7.

The control system 8 generates valve control impulses with a frequency equal to half the network frequency, which are shifted by the phase shifter 9 by the required angle relative to the maximum supply voltage, depending on the current sensor signals 10.

The operation of this converter loaded on an inductive load can be described by the following expression (the moment of time when the mains voltage passes through the maximum value is taken as the reference point):

i: sin 2Q + - sin Wt,

 WL WL

where l is the instantaneous value of the consumed current;

Urn, W, respectively, the amplitude value and the angular frequency of the supply voltage; L is the inductance of the reactor; Q - the initial phase of the pulses

management

As can be seen from the above equation, the current consumption curve contains a constant component

/ z sin 2Q WL

and variable constituent

/ - - sin t,

WL

which does not depend on the magnitude of the angle Q. There are no higher harmonics in the current curve,

As an example (Fig. 3a), the voltage curves on the reactor Lfp (t) (Fig. 36) -current in the reactor ip () and (Fig. 3, c) - network current i (t) are well-suited for the angles Q - (- 15 ° and Q + 45 °. In the latter case, the level of the constant component will be maximum.

FIG. 4 shows a curve depicting the dependence of the magnitude of the constant component (in relative units) on the magnitude and sign of the initial phase of control pulses Q. From this graph it follows that by adjusting the magnitude of this phase from -45 to + 45 °, you can melt be guided (from zero to maximum), and also change the sign of the constant component in the mains curve of the converter. In a similar way, the low-frequency component of the non-linear load network current is compensated: the phase of the control pulses, depending on the signals from the current sensor 10, is changed discretely over a period of the supply voltage.

The use of the present invention will improve the quality of electrical energy in networks with non-linear loads by compensating for a constant

0 or the low-frequency component of the current consumed by these loads, as well as even harmonics arising from the biasing of the constant component of the magnetic circuits of power transformers.

Claims (3)

Invention Formula The control method of a single-phase valve-controlled frequency converter loaded on a reactor with a linear characteristic, the control of which valves is produced with a frequency equal to half the network frequency, characterized in that 5 in order to compensate for the DC or low frequency component of the current consumed by the nonlinear load, they additionally form a DC or low frequency component of the current equal in magnitude and opposite in sign to the analogous component in the current of the nonlinear load, and the phase of the valve control pulses is controlled within from -45 email hail, up to +45 el. hail, in relation to 5 maximum network voltage. Sources of information taken into account in the examination 1. Japan patent No. 48-44971, cl. H 02M 5/26, 1972. 2. USSR author's certificate No. 443446, cl. H 02 M 1/08, 1972. 3. Natent USA 18854, cl. H 02 M5 / 30, 1973. hs-f-jU- i-. npuSlj y -as /. X .x; / 1xX / y , - vuB-rS cji