SU519832A1 - Artificial switching rectifier - Google Patents

Description

one

Known controlled rectifiers with artificial switching of thyristors 1, 2, containing a power thyristor bridge and a forced switching node in the form of an auxiliary diode bridge with a output capacitor and two thyristor switches with capacitor switching, connected between the poles of the power and auxiliary bridges of the same name. However, these circuits can operate in a limited range of loads, since their external characteristics are significantly distorted in the area of low currents.

This drawback is due to the fact that in the inter-switching spacing, the dosage of the switching capacitor from an external source is necessary, which leads to an increase in the voltage across the load in the low-current region and makes the use of such rectifiers unsuitable for a widely controlled electric drive. In addition, a relatively powerful source e is required for charging or discharging a capacitor in dynamic modes of operation of rectifiers. d.

The rectifier described here differs from the known ones in that between the input terminals of said power and auxiliary bridges are included the secondary windings of the booster transformer, the primary windings of which are connected to the input terminals of the power bridge.

This provides the rigidity of the external (or load) characteristics and allows a slight improvement in technical performance by reducing the power of the auxiliary

source dose yes.

FIG. 1 and the presentation diagram of the rectifier; in fig. 2 - time diagrams, which show the work of the rectifier.

The rectifier contains a power bridge 1,

connected by the input terminals to the mains and the output to the load 2. The primary windings of the booster transformer 3 are connected to the input terminals of the power bridge, and its secondary windings

included between the inputs of the power bridge and the auxiliary bridge 4. The output of the bridge 4 includes a capacitor 5. Between the outputs of the power and auxiliary bridges, keys 6 and 7 are included, whose circuits are identical. For

The initial charge of the capacitors and the start-up of the converter serves as a low power auxiliary source 8.

Before starting the straightener operation, the condisator 5 is charged from source 8 to a voltage that is more than the amplitude of the line voltage of the supply network. From the same source, the capacitors CK of keys 6 and 7 are charged through the load and high-resistance resistances that shunt the thyristors

TC (in the diagram, these resistances are not shown). In this case, the capacitor Sk key 6 charges

plus on the right plate, and the key capacitor 7 - plus on the left plate. Both keys work synchronously, so only the operation of key 6 is considered below.

Suppose that the load current 1a flows through the power thyristor in the anode group of the bridge and phase C and the power thyristor in the cathode group of the bridge and phase A (shown in Fig. 1 with solid arrows). Let it be necessary to commute the current into phase B (dotted arrow) at the moment о o (Fig. 2). The thyristor T is turned on, and the capacitor Ck begins to recharge on the circuit “+, CK, G, /) 2, LK, CK. Through the open thyristors T of the keys 6 and 7, the voltage of the capacitor 5 is applied to the load, greater than the amplitude of the line voltage. Nevertheless, the current in phase A cannot immediately disappear, since in the power supply, it always has a network inductance (reactors with a transformerless converter or inductance of the transformer windings). Under the action of ed. with. self-induction and ed with. the network current continues to flow in phase A for some time, but not through the power thyristor of this phase, but through the diode of bridge 4 and thyristor T, since besides the power thyristor, in addition to the diode, a small voltage of the booster transformer 3 is turned on, and this voltage angle range-150 el. hail. email hail, in three-phase circuits and -180 e. hail. email hail, in single-phase circuits directed “plus to the cathode of the lockable power thyristor. Thus, in almost the entire operating range, it is fast, their switching angles of the converter (i.e. during artificial switching, a voltage transformer provides instantaneous current transfer to the circuit of bridge 4, which will be unlocked until the electromagnetic energy accumulated in the inductance LS to the precommutation voltage is consumed period.

In the interval (Fig. 2, a), the sum of two currents flows through the thyristor T: overcharging and SC and the load current. By the time ti Ck, the recharging is completely recharged and the voltage on its plates changes sign (active losses are not taken into account). The thyristor T continues to be unlocked, since a current Id flows through it, equal to the sum of two currents: a decreasing current of phase L (in phase C, the process is identical) and an increasing current of capacitor 5.

At time 3, when the current of phase A is close to zero, and the current of capacitor 5 almost reaches the load current Id, Hk turns on and an oscillatory overcharge occurs. D SC, during which the current in T drops to zero (time t and for a time / in thyristor T is locked (in recovery time). In interval 5, all the load current goes through the capacitor 5 and the shifted diode Di. At the moment d, the recharge current and SC becomes less than the load current, DI is locked. At the same time, an unlocking pulse is applied to the power thyristor of phase B in the cathode group (pulse on the power thyristor of the phase C one group is available with "wide control pulses or is transmitted repeatedly through 60 e. hail, with narrow control pulses.) Since at the moment the diode D is closed, the load current under the action of the self-induction eds is not interrupted, but will go two branches: via C, completing its recharging, and through phases C and B, to which a capacitor 5 is connected via bridge 4.

Due to its small capacitance, the capacitance on Sc increases rapidly as compared with the capacitor 5, the current in the CK circuit becomes zero by the time t (the axis of this current is displaced relative to the axis / in Fig. 2, a). The current in B and C cannot instantly increase due to LS inductance, therefore from the moment t the load current goes but to two branches m: through the capacitor 5, gradually decreasing, and through the network phases, gradually the age. When the current in phases B and C becomes equal to the load current, the current through the capacitor 5 drops to zero, the switching is completed. If we neglect the active losses and assume Ld Ls (Ld-load inductance), which is always fulfilled in the medium and high power electric drive, it is obvious that the energy consumed by the capacitor 5 at the first stage will be returned back at the second stage and the voltage of the capacitor 5 will be restored.

In | transient conditions, the load current can quickly change from zero to the maximum value. In this case, in the known circuits, the capacitor 5 may not have time to charge in the inter-switching time interval (this interval in the dynamics also changes) to a voltage greater than the linear amplitude. Then the switching failure is inevitable. To avoid it in the well-known schemes, it is necessary to increase the power of source 8 to the great distance:

(Af / ,, + f / ,, (1)

where C / lto is the amplitude of the linear voltage;

 - an extra few volts necessary to ensure the commutation of power thyristors.

In the proposed scheme, the same effect is achieved using a booster transformer, the power of which is:

, „“ (If / l g + l ™) /.shah- (12)

In this case, the source 8 is needed only for starting the circuit, its power is negligible (fractions of a watt) and is determined only by the leakage currents Sk and the capacitor 5.

Claims (2)

It should be noted that keys 6 and 7 are implemented using a typical LC switching circuit (see, for example, the book Zabrodin Yu. S. “Nodes of capacitive switching of thyristors. Energy. M. 1974, fig. 1-5,6). Another variant of the key scheme is possible, however, in order to ensure the hard load characteristics of the converter, it is necessary that the operation of the keys does not affect the magnitude of the rectified load voltage. In received key circuits, this is ensured by recharging the CK through the closed channel through the reverse diodes DI and DZ, i.e., the voltage generated by the keys in the external circuit is practically zero. A further advantage of the proposed rectifier is the possibility of significantly reducing the dimensions of the keys; Tk and T can be chosen with a short recovery time, which will reduce Sk and LK, while the power thyristors can be with any recovery time. Their locking is ensured by a unipolar capacitor 5, operating in the mode of a partial charge of the discharge (see Fig. 2.6). The proposed artificial switching rectifier circuit favorably differs from the known rigid load characteristics and low power of the auxiliary source. 6 The invention rectifier with artificial switching, containing a power thyristor-bridge and a forced switching node in the form of an auxiliary diode bridge with a capacitor at the output and two thyristor switches connected between the poles of the power and auxiliary bridges of the same name, characterized in that, in order to increase the stiffness of the load characteristics and the improvement of technical performance, between the input terminals of these power and auxiliary bridges include the secondary winding of the booster transformer, the primary windings of which are connected to the input terminals of the power bridge. Sources of information taken into account in the examination: 1. Yu. M. Bozhin, G. S. Mytsyk: “On the possibilities of using compensatory rectifiers. Proceedings of MEI, vol. 147, 1972, pp. 49-53. 2. Auth. St. No. 319999 H 02M 7/12. Aff C