RU1820987C - Frequency-controlled electric drive - Google Patents

Abstract

Usage: in electric drives, the speed of which is controlled by an inverter. SUBSTANCE: device contains an inverter powered through a fully controlled key - a transistor from a direct current source. The means by which, when the inverter is disconnected from the source, are the introduction of either a non-return valve or a capacitor into the circuit of self-induction currents, the thyristors of the second additional bridge. 2 ill.

Description

The invention relates to an electric drive, the engine speed of which is controlled by an inverter powered by a constant current source.

The purpose of the invention is to reduce the cost, dimensions and increase the reliability of the variable frequency drive, which is achieved by using thyristors as the valves of the second bridge, the input terminals of the first thyristor bridge connected by capacitors to the input terminals of the same name, positive and negative, the second bridge connecting the non-return valve .

In FIG. 1 presents a diagram of the proposed electric drive; in FIG. 2 is a diagram of a prototype electric drive.

In FIG. 1 thyristor bridge, consisting of 1-6 thyristors, is connected to a constant current source 7 through a transistor 8. A source 7 can be a rectifier

(controlled or uncontrolled), and the accumulator C / 1. A second bridge on thyristors 11-16 is connected to the first thyristor bridge f through capacitors 9-10, the input of which is shunted by a check valve 17. The outputs of the bridges are combined and connected to them Motor windings 18.

In the prototype electric drive (FIG. 2), the thyristor bridge is connected to the DC source 7 10 not only through transistor 8, but also through transistor 19, and QQ 20 is connected in parallel with source 7. Instead of an additional bridge on thiagors 11-16 in the prototype electric drive there is a bridge of check valves 21-26.

According to the circuit of FIG. 1 we consider the work Ј of the proposed electric drive for the case when the task is not to ensure the sinusoidality of the motor currents and purpose; bridges is reduced to changes in the direction of currents in the windings of the motor 18 in accordance with a given frequency of supply

engine The establishment of the required supply voltage is provided either by regulating the source 7 or by the latitudinal modulation of the base current of the transistor 8. Let us first consider the operation of switching the control currents of thyristors 11-16 when the latitudinal modulation of the current of the base of the transistor 8 is carried out in order to establish the required voltage, i.e. when the gate 17 must be introduced into the circuit of the self-induction currents, we believe that the high-speed valve 17 and the thyristors 11-16 are used. Let in the period between two changes in the direction of the currents in the winding motor 18, that is, over 1/6 of the output frequency, the directions of the currents in phases correspond to the solid arrows in Fig. 1. Then, and this period of time, the control currents of the thyristors 1,3,6 of the first bridge should be constantly on, and before breaking transistors 8 of the source 7 circuit must supply short pulses of control currents to the corresponding thyristors of the second Bridge, that is, to thyristors 11, 13, 16. Then, when the source 7 is turned off, the self-induction currents of phases A and B are transferred from thyristors 1,3,6 of the first bridge on thyristors 11, 13, 16, the second bridge and it is closed through a non-return valve 17 (de-energization of thyristors 1,3,6 will occur because the circuits with series-connected capacitors 9, 10 and thyristors 1,3,6 will turn out to be shunted thyristors .11, 13,1-6). When the source circuit 7 is subsequently closed, thyristors 1,3,6 are turned on and thyristors 11, 13, 16 are turned off, i.e., the current distribution is restored. Let the time period under consideration end with a reversal of the current in phase A indicated by the dashed arrow. When the transistor 8 was last turned on during this period of time, the thyristor control current 1 m is turned off; only the thyristors 13.16, but not the thyristor 11, are turned on. Before turning off the transistor 9, a time delay is set to restore the blocking properties of the thyristor 11 (this delay is obtained automatically, if the period of the latitudinal modulation of the transistor 8 is longer than the restoration time of the locking properties of the thyristors 11-16). Then, when the transistor 8 is turned off, the phase B current will be transferred from thyristors 3, 6. to thyristors 13, 16 and will be closed by the circuit: phase B - phase C - thyristor 16 - check valve 17 - thyristor 13 - phase B. The current of phase A phase will be closed by chains: phase A - phase. C - thyristor 16 - check valve 17 - capacitor 9 - thyristor 1 - phase A. When this circuit is formed

the capacitor 9 will be charged with current b with the direction of the charging EU EMF indicated by the dotted arrow. After the moment the transistor 8 is turned off

switching time tn to + te, the control current of thyristor 2 and transistor 8 can be turned on (to is the current decay time to zero; tv is the time to restore the locking properties of the thyristors). This should remain

Thyristor 3 is turned on, through which the total current of phases A, C will flow. Thus, with a new combination of current directions, thyristors 2, 6, 3, s turn on in the first bridge

5 by switching on of which transistor 8 and capacitor 9 with a charged EMF It will be discharged along the circuit: source 7 - capacitor 9 - thyristor 13 - phase B - phase A, phase C - thyristor 2, thyristor 6 - transistor 8 0 source 7. When this, through the thyristor 3 with the control current turned on, 1b will not flow, since this thyristor is biased by the EMF Ec through the thyristor 13 in a non-conducting direction. When the capacitor is sized up to 0, thyristor 3 is included in the total current circuit, and thyristor 13 with a previously switched off control current is turned off from this circuit (if the used valve 17 and thyristor 11-16 do not have

0 with sufficient speed, parallel to the valve 17, a capacitor with a current-limiting resistor must be connected, which receives the inductance energy ca5 in series with the capacitors 9, 10 from the time the transistor 8 is turned off until the delay time for turning on the valve 17 and thyristors 11-16 expire. This time may be of the order of ten microseconds). These extra

0, a capacitor with a resistor is shown in broken lines in FIG. 1.

We now formulate a control algorithm for each 1/6 of the period of the output frequency, over which

The 5 current directions remain unchanged. The control currents of the respective thyristors 1-6 of the first bridge are kept constant on; and the control currents of the respective thyristors 11-16 of the second bridge

0 turn on only a little earlier shutdown of the source 7 and only for a while before the appearance of current in them. A change in the direction of the current of any of the phases begins before the next turn off of the transistor 8 with 5 turning off the control current of the thyristor of the first bridge related to the switched phase and turning on the control current of two thyristors of the second bridge related to the phase with the direction unchanged for a given period of time current, after which the transistor 8 is turned off. After the time of charging the capacitor and the time to restore the locking properties of the disconnected thyristor of the first bridge, the control current of the antiphase thyristor is turned on pa and the transistor 8, a source of NO 7 chain.

The definition of the control algorithm for thyristors 11-16 of the second bridge in each specified 1/6 of the period of the output frequency during the formation of sinusoidal currents of two phases of the same direction, and therefore the sinusoidal total current of the third phase, is based on alternating fast current decay when one of the capacitors 9, 10 is introduced into the self-induction current circuit and slow decays when the non-return valve 17 is introduced into this circuit. Such a formation is possible, since the mode is selected every time the transistor 8 is turned off and the current drop for one of these two phases can be produced independently of the other phase.

Let us now turn to a comparison of the proposed electric drive with the electric drive prototype (figure 2). The electric drive of FIG. 1 has the following advantages over a prototype electric drive: a) lower cost. A power transistor for operation in rectified mains circuits (e.g. 540 V) is significantly more expensive than a thyristor for the same throughput power. In the prototype electric drive, the rated voltage of the capacitor should be selected approximately by the value of the mains voltage greater than the rated voltage of each of the capacitors 9, 10. In the prototype electric drive there are six high-speed check valves, one of which is proposed. In the case of non-performing valves, each of these six valves must be bridged by its own capacitor-resistor circuit. Therefore, the total cost

elements of the circuit in figure 1 will be lower than in figure 2.

b) a simpler control algorithm. In the prototype electric drive (FIG. 2), it is difficult to introduce a self-induction capacitor 20 into the current circuit. Let the capacitor, for example, be inserted into the phase A circuit. To do this, turn off the transistor 19, and then remove the thyristor 1 from the current circuit of the phase A. In this case, the current is closed in the circuit: phase A - phase C - thyristor 6 - transistor 8 - valve 22 - phase A. After restoring the thyristor's locking properties, it is necessary to turn on transistor 19 again so that it does not interrupt b during the next operation. and only then turn off the transistor 8, input to the current circuit Is a capacitor in the circuit; phase A - phase C - valve 25 - capacitor 20 - valve 22 - phase A. Thus, an unnecessary turn-off of the transistor 19 is necessary compared to Fig. 1, the duration of which is equal to the time of restoration of the locking properties of the thyristor 1.

c) greater reliability. This follows from items a), b).

Claims (1)

SUMMARY OF THE INVENTION A variable frequency drive comprising a constant current source connected through a semiconductor switch to the corresponding input terminals of the first thyristor bridge, the output terminals of which are connected in phase to the output terminals of the second valve bridge and to the motor winding terminals, characterized in that in order to reduce cost, dimensions and increase reliability, thyristors are used as valves of the second bridge, the input terminals of the first thyristor bridge are connected to ndensatorami with similar input terminals, positive and negative, the second bridge between which included inputted return valve. , 2m II4Sh1 11 // Zs ffi / / about fS / .   f 2 f 1-: t / W; at M / t 2 & A 2 L ZG / S / 7 J