RU2281604C1 - Transformer-load thyristor switch - Google Patents

Abstract

FIELD: electrical engineering; switching single-phase transformer load.

SUBSTANCE: thyristor switch control system is provided with rectangular hysteresis loop pulse transformer and noise-suppressing circuits inserted in thyristor switch control circuit. Control system saves information in its memory during intervals in power supply for unlimited time intervals and eliminates inrush magnetizing current when equipment is turned on upon mentioned intervals.

EFFECT: eliminated inrush magnetizing currents in electric circuit reclosure.

1 cl, 3 dwg

Description

The invention relates to the field of electrical engineering, in particular to thyristor load switches of predominantly transformer type, operating in intermittent mode with a large number of starts per minute.

For switching such loads, i.e. to turn on / off, thyristors or triacs are currently used. Their advantages over electromagnetic contactors are well known and are especially pronounced precisely at a high switching frequency.

An example is thyristor "contactors" for switching welding transformers in resistance welding machines, where the duration of the on and pause intervals from one to tens of hertz. Microwave ovens and the like installations in which it is advisable to use a thyristor switch in the primary winding circuit of a transformer supplying a load have a rather high switching frequency, especially in low-temperature heating modes.

It is known that the inclusion of a transformer in the network is accompanied by a surge of magnetizing current, the value of which reaches ten times the value of the rated current. To minimize or completely eliminate the inrush current at the moment of turning on the transformer, the thyristor switch control system is synchronized with the mains supply, and the on-off trigger included in this system in known devices [1] provides for “memorizing” the sign (plus or minus) of the last half-period of the current. The next inclusion of the transformer is possible only in the half-cycle with the opposite sign. Thus, an even number of half-periods of current passes through the transformer and the magnetization of the transformer is eliminated. Synchronization of the control system with the network also provides an optimal starting angle for turning on the thyristor switch.

Similar control systems for thyristor switches are used in recent years [2]. In particular, in the catalog of the company FORWEL, 2004, Paqe 1 of 6 provides a control system for machines for resistance welding (i.e. resistance welding), a simplified functional diagram of which is shown in figure 1.

The control device of a thyristor switch with a two-position trigger (Fig. 1) contains a single-phase transformer 1 in the power circuit, connected to the network through a thyristor switch of two on-parallel thyristors 2, 3 and a control system for the said switch as part of a pulse transformer 4, two secondary windings which through diodes 5, 6 are connected to the corresponding control inputs of the mentioned thyristors 3, 4, and the primary winding of the pulse transformer 4 is connected to the output of the on-off trigger 7 and connected at its one input to the power supply 8 and the second input to the output of the pulse-base system controller 9, synchronized via the power supply mains 8 and is connected to its control input to the automatic control system 10.

The described device is the closest device of the same purpose to the claimed invention according to the totality of features and is adopted as a prototype.

The reasons that impede the achievement of the technical result indicated below, both in the aforementioned analogues and in the prototype, are memory loss by a two-position trigger when the mains voltage disappears due to an accidental or operational shutdown.

EFFECT: saving the memory of the thyristor switch control device at any interruptions in power supply and, as a result, eliminating the inrush of magnetizing current when the device is turned on after the mentioned interruptions in power supply.

The specified technical result during the implementation of the invention is achieved by the fact that in the known device containing a single-phase transformer connected to the network by a thyristor switch of two on-parallel thyristors and a control system of the said thyristor switch as part of a pulse transformer, the primary winding of which is connected to the output a pulse-phase control system synchronized by means of a power supply unit with a power supply network and a connected control input automatic regulation system, the pulse transformer is made on the core with a rectangular hysteresis loop, its secondary windings are connected to two corresponding control inputs of the thyristor switch thyristors through identical noise suppression chains, each of which contains a resistor and a dynistor connected in series, connected by an anode to a resistor, and a cathode to a control an electrode of the corresponding thyristor of said thyristor switch. With a free terminal, the resistor is connected to the corresponding terminal of its secondary winding of the pulse transformer, the second terminal of which is connected to the cathode of the corresponding thyristor of the thyristor switch, and a capacitor is connected between the common point of the resistor and the dynistor and the cathode of the corresponding thyristor. This made it possible to preserve the device’s memory during any interruptions in the power supply and, as a result, eliminate the magnetizing current surges when the device is turned on after interruptions in the power supply, as well as to combine the memory and galvanic isolation functions in a pulse transformer, excluding the two-position trigger from the circuit.

The invention is illustrated in figure 2, which shows a diagram of a thyristor switch transformer load on the example of a welding transformer for resistance welding. Information confirming the possibility of carrying out the invention are as follows.

The device (figure 2) contains in the power part a single-phase welding transformer 1 connected to the network through a thyristor switch from two counter-parallel connected thyristors 2 and 3. The secondary winding of the welding transformer 1 is closed to a load, for example, to the welded parts.

The device control system consists of a pulse transformer 4, the secondary windings of which are connected to the corresponding control inputs of the aforementioned thyristors 2 and 3, and the primary winding is connected directly to the output of the pulse-phase control system 5, synchronized through the power supply unit 6 with the supply network and connected to the control input to automatic regulation system 7. The pulse transformer 4 is made on a core with a rectangular hysteresis loop, and its two secondary windings are connected are connected to the corresponding control inputs of thyristors 2 and 3 of the thyristor switch through identical noise suppression chains. Each of the noise suppressing chains contains a resistor 8 and a dynistor 9 connected in series with a resistor 8, and a cathode with a control electrode of a thyristor 2 in one chain and the same resistor 10 and a dynistor 11 connected in a similar way, and the cathode of the dinistor 11 is respectively connected to the control electrode thyristor 3.

The mentioned resistors 8 and 10 are connected by their free terminals to the corresponding terminals of their secondary windings of the pulse transformer 4, and the free terminals of the secondary windings of the pulse transformer 4 are connected to the cathodes of the respective thyristors 2 and 3. Between the common point of the dinistor and the resistor in each of the noise suppressing chains and the cathode of the corresponding thyristor thyristor switch included capacitors 12 and 13.

The device operates as follows.

When the device is connected to the supply network through the power supply unit 6, a voltage (with an appropriate transformation ratio) is supplied to the pulse-phase control system 5, which is processed into a sequence of bipolar pulses (magnetization reversal diagrams of a pulse transformer - a change in its voltage U in the function wt and induction B in the function of ampere-turns iW of the pulse transformer winding, see figure 3). The necessary initial angle of delay of these pulses is provided by the automatic control system 7, as in all known devices of a similar purpose. The first pulse, depending on its polarity, includes one of the thyristors, for example, thyristor 2. At the same time, this pulse is transferred to saturation mode, for example, to point 1 in figure 3, pulse transformer 4. After the disappearance of the pulse, the core of the transformer remains magnetized at point 2 , i.e. remains saturated due to the rectangularity of the hysteresis loop. This state of the pulse transformer core will remain until a pulse of opposite polarity arrives, which magnetizes the core to point 3 and simultaneously turns on the thyristor 3, and the core remains magnetized at point 4. When the mains voltage disappears, the pulse transformer core will retain magnetization from the last pulse for an arbitrarily long time, therefore, when voltage is restored to the thyristors, only the pulse with the polarity opposite to the last pulse before switching off can be the first to pass m networks. In other words, if thyristor 2 was last turned on (Fig. 2), then after restoration of voltage through any arbitrary time interval, only thyristor 3 can turn on first. Accordingly, even an even number of half-periods of current will always pass through transformer 1 (Fig. 2), t .e. it will be remagnetized by a symmetrical hysteresis loop, no matter what the network shutdown intervals are.

Thus, even short-time magnetization of the power (in the considered welding example) transformer is excluded and, accordingly, surges of the magnetizing current after pauses in the power supply of the installation are excluded.

Since the rectangularity of the hysteresis loop of known ferromagnetic cores is not ideal, the transition from the saturation point to the point of residual magnetization (Fig. 3) is accompanied by a small difference in induction ΔВ and, accordingly, a short-duration interference pulse in the windings of a pulse transformer, which could "falsely" turn on one of the switch thyristors. In order not to miss the interference pulse to the thyristor control input, the aforementioned noise suppression chains are used: when such a “false” pulse occurs, capacitors 12 and 13 are shunted due to the small difference in induction ΔВ (Fig. 3), the voltage integral of the “false” pulses is negligible and, accordingly, the value (amplitude) voltage from these pulses is small and insufficient to switch to the conductive state of the dynistors 9 and 11. This eliminates the "false" inclusion of thyristors of the switch. At the same time, “working” pulses have a sufficiently large width dictated by the requirements of the load. Devices that provide the desired width of the working pulses are widely known, are included in the package of the pulse-phase control system and are not shown in FIG. 2 for simplicity.

In conclusion, it should be noted that the proposed device simultaneously with the solution of the technical problem poses, it can somewhat simplify the circuit by excluding the on-off “memory” trigger.

Information sources

1. Glebov L.V. etc. Calculation and design of resistance welding machines. Energy Publishing House, Leningrad, 1981.- 424 p. Fig. 8-4, 8-5.

2. FORWEL Company Directory (2004), Paqe 1, of 6 (p. 1, section 6) - Resistance Welding Control. Fig. 1.

Claims (1)

A thyristor switch of transformer load, comprising a single-phase transformer in the power circuit, connected to the network by a thyristor switch of two on-parallel thyristors, and a control system for the said thyristor switch as part of a pulse transformer, the primary winding of which is connected to the output of the pulse-phase control system, synchronized by power supply unit with mains and connected control input to the automatic control system, characterized by m, that the pulse transformer is made on the core with a rectangular hysteresis loop, its two secondary windings are connected to two corresponding control inputs of the thyristor switch thyristors through two identical noise suppressing chains, each of which contains a resistor and a dynistor connected in series, connected by an anode to a resistor, and the cathode - with a control electrode of the corresponding thyristor of the said thyristor switch, with a free output resistor connected to the corresponding output its secondary winding of the pulse transformer, the second output of which is connected to the cathode of the corresponding thyristor of the thyristor switch, and a capacitor is connected in each noise suppressing chain between the common point of the resistor and the dynistor and the cathode of the corresponding thyristor.

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