FI75069B - OEVERVAKNINGSENHET FOER KORTSLUTNING I EN TYRISTORBRYGGA. - Google Patents

Description

75069

THYRISTOR BRIDGE SHORT CIRCUIT CONTROL UNIT - ÖVERVAKNINGSENHET FÖR KORTSLUTNING I EN TYRISTORBRYGGA

The present invention relates to a thyristor bridge short-circuit monitoring unit in AC-supplied thyristor drives in which one or more thyristor bridges supply a motor, and which monitoring unit includes current measuring electronics.

With the development of semiconductor technology, motor control has increasingly shifted to thyristor technology. There are several benefits to this. However, one of the drawbacks remains the sensitivity of the thyristor systems to fuses. Especially in four-quadrant thyristor drives, in the case of bias-ignition of thyristors, there is a so-called danger of internal short circuit. This is shown in Figure 1, where a short circuit is indicated by arrows. In the event of a short circuit, the fuses protecting the thyristors usually burn out. Especially in elevators, for example, such a molten peripheral disturbance causes unpleasant downtime.

The object of the present invention is to eliminate the above-mentioned drawbacks. The control unit according to the invention is characterized in that in the short-circuit situation the ignition pulses of the thyristors can be removed by the control circuit in the control unit by directing current By means of the invention, the above-mentioned fuses caused by short circuits can no longer occur. The short-circuit condition is detected by a current measurement and this information removes the ignition pulses of the thyristors, after which the magnitude of the current pulse is limited to a safe value for the thyristors and fuses by means of series chokes, and the device is ready for operation. A control circuit like this is simple, secure and inexpensive.

A preferred embodiment of the invention is characterized in that the power supply to the igniter unit can be switched off by means of a transistor on the basis of the signal received from the comparator.

Another preferred embodiment of the invention is characterized in that the series chokes are air-core.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which

Figure 1 shows a thyristor bridge known per se.

Figure 2 shows a control unit according to the invention connected to its thyristor.

* · * · * Figure 3 shows the connection of the monitoring circuit.

Figure 4 shows the current curve as a function of time.

-: **. · Figure 2 shows an example of a motor drive in which bridges S1 and S2 control a DC motor. The current of the bridges is measured by the current transformers 1a, 2 and 3. The current information given by the current transformers is converted into a signal corresponding to the motor current by a conventional 11a rectifier in block VM. The output voltage Uv of the block VM corresponds. system power status. In Fig. 3, the operator is reinforced. *: ·. **** opi, which acts as a comparator indicating the hip. If the current information Uv exceeds the resistors R1 and R2 ____. determined by the measurement threshold so the output of the amplifier changes. . .1. negative and disarms the transistor T1 by means of the energy "." Is igniter strategy to pass. Power off half • • during the network cycle. This is due to the physics of the phenomenon, referred to herein need not be considered further. However, it is noted that the current pulse is determined according series choke L1 inductance. The choke cannot be practically iron-core, however, the short-circuit current peak ·· *. Is relatively large and it saturates the normal-sized iron core choke. that they always limit the short-circuit current to less than the peak value of the surge current Itsm.

The igniter unit may be of a conventional generally known construction. The function of the resistor R3 of the diode D1 and the capacitor C1 is to prolong the current measuring pulse. By adjusting the magnitude of C1, the switch-off time can be adjusted. Usually, a short circuit is rare, so the equipment will continue to operate after the short circuit situation has passed.

It will be apparent to one skilled in the art that various embodiments of the invention may vary within the scope of the claims set forth below.

Claims (3)

75069 1. Short-circuit monitoring unit for a thyristor bridge in AC-fed thyristor drives in which one or more thyristor bridges supply a motor, the control unit comprising current measuring electronics (VM), characterized in that in a short-circuit situation current information (Uv) to the comparator (learn) in the control circuit (VE) and switching off the energy supply (Is) to the igniter unit based on the signal from the comparator (learn), and that the supply voltage has series chokes (LI) limiting the magnitude of the short-circuit current pulse. »A • · · Short-circuit monitoring unit according to Claim 1, characterized in that the energy supply (Is) to the igniter unit can be switched off by means of a transistor (T1) on the basis of a signal from the comparator. Short-circuit monitoring unit according to Claim 1 or 2, characterized in that the series chokes (LI) are air-core. * · · * · · · «II