SK9202001A3 - Method and device for protecting converters - Google Patents

Abstract

Under braking conditions, the power supply to the drive motors from the inverter assembly is prone to hashing. The protection circuit causes a half cycling of the supply voltage under these conditions to generate a hashing function during the braking procedure. The hashing function limits the peak surge of the supply voltage. An Independent claim is included for an installation utilizing the described circuit protection system.

Description

In particular, the invention relates to a method comprising a voltage protection function of the converter and a function of intermittent braking in the propulsion chain.

The invention also relates to an apparatus which implements the method.

BACKGROUND OF THE INVENTION

Electric drive motors, such as synchronous, asynchronous and even DC motors, are equipped with converters. One example is a voltage converter that allows to obtain AC voltage from a DC voltage from the overhead contact line. To supply power to a load consisting of electric propulsion motors, which are three-phase motors, it is necessary to provide a three-phase voltage system that is closest to a balanced, frequency variable and amplitude variable sinusoidal three-phase system. A DC / AC converter is a device that enables this goal to be achieved and uses power components for this purpose, such as thyristors, GTO thyristors, and the like.

Until now, semiconductors, which are used as switches in transducers, and in particular in converters, tolerate a voltage that is greater than the voltage in the overhead contact line.

In the specific case, for a nominal DC 3 KV overhead contact line, for example, it is recommended to use two GTO thyristors with a value of 4.5 KV connected in series. This provides a large safety margin which allows the voltage of the inverter terminals to be maintained, in each working case.

In addition, if the converter is blocked, for example due to overvoltage in the overhead contact line, an instantaneous overvoltage also appears at the inverter input. This overvoltage essentially depends on the parameters of the converter itself, the input filter, any current interruption and the parameters in the overhead contact line itself.

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-2 (Corrected Sheet)

Recently, new types of static switches have appeared. These include static IGBT switches (isolated gate bipolar transistors), MGT transistors, IGCT transistors, and the like. In general, these devices can be supplemented by the use of mechanical vibration limiters, if the control is realized by a gate.

The use of this new generation of semiconductors, especially when using the IGBT type, allows a reduced maximum voltage to be allowed. The reason is that it is enough for inclusion

3.3 KV IGBT in series when there is a 3 KV voltage in the overhead contact line. This means that the safety range also decreases, resulting in the need to use a protective device to limit the voltage of the converter input filter to ensure that the maximum voltage at the semiconductor terminals never exceeds their maximum value. The principle of such a protective system is simple and includes a protective device connected when the voltage exceeds the maximum threshold value, but does not disconnect until the voltage drops below the minimum threshold value. The need to include a voltage limiting protective device requires the use of an electrical appliance at the input of the converter, which in practice means any resistance.

They are usually used as an accessory at the filter inlet, - located in front of the transducer, with pulse transducers, in particular cases with a breaker. SUMMARY OF THE INVENTION

It is an object of the present invention to provide new generation switches, for example of the IGBT type for converters, as well as a protective device.

The present invention also provides a device for implementing a method that makes it possible to rationally use the device to control braking and overvoltage protection at the inlet of a converter supplying power to the motors.

The invention relates to an apparatus for supplying power to a propulsion motor representing a load starting with a DC power supply, providing a source through a transducer and overvoltage protection means by a voltage limiting means that includes resistors for dissipating excess voltage, further comprising braking. .

The resistors used to dissipate the braking current, the device being characterized in that the resistances of said overvoltage protection means by voltage limiting and the braking resistors are the same resistors arranged in separate circuits arranged in parallel.

In a particularly advanced method, resistors are supplied with electricity alternately during braking and simultaneously with voltage limitation.

More specifically, each resistor is connected in series to a separate control semiconductor.

According to one preferred embodiment, the at least two controlling semiconductors, each connected to at least one resistor, are connected to an intermediate point of the DC network, the resistors being coupled in pair to both poles of the network.

According to another preferred embodiment, the resistors are connected in series with the current-controlling semiconductors in the forward direction.

In addition, each resistor (usually) is connected in parallel to a zero-current blocking diode in the forward direction.

The invention also relates to a method of supplying electric power to a propulsion motor which generates a load (M) starting at a DC network generating a source by means of said device, and by means of which controlling semiconductors of said resistors are alternately controlled by braking and voltage limitation.

In a particularly advanced method, said controlling semiconductors are alternately controlled by the interleaving system.

Overview of the figures in the drawing

Fig. 1 is a schematic view of a propulsion chain comprising various power circuits and modules, such as input circuit, input filter, brake chopper, converter and electric propulsion motor, when prior art switches have been used; Fig. 2 schematically illustrates a view of the breaker in the case where new generation switches, such as IGBTs have been used; Fig. 3 schematically shows a view of a protective device operating on the principle of restraint to be used when a new generation of switches such as IGBTs are used in the propulsion chain (FIG. 1); Fig. 4 _3α.

(Corrected sheet) schematically illustrates a view of a solution according to the present invention combining the function of a brake interrupter and a voltage limiter; Fig. 5 and 6 illustrate the principles of operating the breaker and voltage limiter.

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Examples of embodiments of the invention

Fig. 1 shows the complete propulsion chain of two propulsion engines M1 and M2. According to the embodiment of FIG. 1 has a three-level converter E, located in front of the three-phase propulsion motors M1 and M2. three branches supplying the three phases R, S, and T of the motors, the breaker C and the inlet filter A, which is directly connected to the O input circuit with 3000 V overhead contact line and rail 16. Typically, the individual components of the GTO thyristors) that do not require the use of an additional voltage protection device (limiter).

If new generation switches such as IGBT type are used, two IGBT transistors in each branch must be used, in case of using 3000 V overhead contact line, in order to withstand the respective load. In this case, both IGBTs are arranged in parallel and connected in series with a braking resistor. As already mentioned, the protective device shown in FIG. 3, which would limit the input filter and converter voltage. Usually each branch consists of an IGBT switch connected in series to the diode and parallel to the limiting resistor.

In practice, when braking, when the voltage between L1 points (connected to the overhead contact line through the inlet filter) and L2 point (in conjunction with the rails) is higher than the threshold, this means that the line can no longer restore the braking energy, capacitance resistors 3 and 4 are limited by activating the controlling semiconductors 5 and 6. These semiconductors divert current to the interrupting resistors 7 and 8.

The intermediate point L3 located between the semiconductors 5 and 6 is connected to the intermediate point L4 between the capacitances 3 and 4 of the input filter A.

The breaker B is suitable for most traction converters and is designed for high performance.

In order to reduce costs, a solution (Fig. 4) is proposed which combines the functions of the breaker and voltage limiter within one power device.

Resistors 7 and 8 are divided into 11+. 12+. 11-, and 12-. IGBT semiconductors supplying resistors and connected in series are also divided into: 13+. 14+. 13-, and HL. Unfortunately, the rated power of the device to act as a limiter requires a low-limiting resistor to provide good voltage protection for the limiter and converter semiconductors (not shown in Figures 2 and 4) must be connected.

-fk by terminals L5 and L6. The use of a low value resistor that is suitable for limiting causes an excessive increase in current value and thus excessive losses in the device when acting as a breaker.

According to the invention, the solution consists in alternating activation of the current passing through the resistors as long as they function as a breaker of the brake.

If the breaker C acts as a voltage limiter, then the heat dissipated in the resistors is less because of the shorter operating time. In this case, the pairs of controlling semiconductors are 13+, 14+. 13-, and 14- excited simultaneously and resistors 11+, 12+. 13-, and 14- are supplied in parallel so that the equivalent resistance between points L1 and L2 has half the equivalent resistance obtained when operating as a breaker.

It should be taken into account that for a given application as a breaker, the resistance is not oversized, it consists simply of two separate parts.

The invention makes it possible to reduce the switching frequency of the semiconductors acting as brake interrupters without modifying the frequency at the capacitance of the inlet filter. Thus, the switching losses in the frequency interrupter are reduced.

In this way, it is possible to take advantage of the alternating mode operation (stepwise processing).

In addition, the current-carrying losses do not increase as a result of the disconnection of the resistance supplied by each of the controlling semiconductors, the current is guided by half, while this current is conducted twice by the alternating operation of the controlling semiconductors.

If, on the other hand, it acts as a voltage limiter, the equivalent resistance value is reduced by half, thereby allowing, by means of a double current, to provide effective voltage protection.

The principle of functioning as a brake interrupter is shown in the graph of FIG. 4 in relation (by way of example) to the controlling semiconductors 13+ and 14+, which operate in alternation. During time period T, semiconductor 13+ operates at time δΤ / 2, starting from time value = 0, while semiconductor 14+ operates at the same time δΤ / 2 starting at T / 2. The duration δΤ / 2 is given by the magnitude of the interrupting effect realized, which means the power lost.

Fig. 5 illustrates the simultaneous action, at each time value T, of the 13+ and 14+ semiconductors during δΤ when acting as voltage limiters.

According to the present invention, the limitation must take place when the voltage exceeds the maximum carrying threshold of the breaker C and / or converter E semiconductors, due to the overvoltage on the overhead contact line 15 or, in particular, to the converter blocking.

In this case, the electronic control device blocks the traction converter E, it starts to operate as a limiter, even if it is not necessary to act as a brake interrupter.

The limiter conducts current to resistors arranged in parallel, switches at a high threshold value and switches off at a low threshold, keeping the voltage below the maximum value and the safe threshold value of the semiconductor voltage. It is the time that elapses between the transition of these two thresholds, which determines the duration δΤ (Fig. 5). If the operation exceeds a given duration value, an additional safety measure will ensure the opening of the overhead contact circuit breaker in the input circuit D.

Provision is made for the possibility of using a device that does not need to be re-treated by a contactor, as the electronics automatically makes this adjustment.

The described embodiment is based on the use of a three-level converter. It will be understood that the above method can be applied by a person skilled in the art to a two-level converter without difficulty, yet such application remains within the scope of the present invention.

Office Van Malderen (Fixed Claims)

Claims (7)

A device for supplying power to a load propulsion motor (M) starting at a DC power supply generates a source by means of a transducer (E) and bias protection means by way of a voltage limiting (B) that includes resistors for removing excess voltage, further comprising braking resistors for dissipating the braking current, wherein the device is characterized in that the resistances of said overvoltage protection means by voltage limiting and braking resistors (11+, 12+, 11-, 12-) are parallel in separate circuits and alternately supplied with current for braking and voltage limiting. Device according to claim 1, characterized in that each resistor (11+, 12+, 11-, 12-) is connected in series to individual control semiconductors (13+, 14+, 13-, 14-). Device according to claim 2, characterized in that at least two controlling semiconductors (134-, 14+, 13-, 14-), each connected to at least one resistor (11+, 12+, 11-, 12-), are connected to an intermediate point (L3) of said network CD, said resistors being coupled in pair to the two poles of the network (L1, L2). Device according to any one of claims 1 or 2, characterized in that said resistors (11+, 12+, 11-, 12-) are connected in series to the current-controlling semiconductors (13+, 14+, 13-, 14-). in the forward direction, i.e. from the positive pole (L1) to the negative pole (L2). Device according to any one of claims 2 to 4, characterized in that each of said resistors (11 +, 12 +, 11-, 12-) is connected in parallel to a diode (9 or 10) which blocks the current in the forward direction, which is the direction from the positive pole (L1) to the negative pole (L2). -8 (Fixed Claims) A method of supplying power to a propulsion motor that generates a load (M) starting at a DC network and generating a source using the device of any preceding claim, characterized in that the controlling semiconductors (13+, 14+, 13-, 14) are used. -) The mentioned resistors (11+, 12+, 11-, 12-) are alternately controlled by braking while limiting the voltage. Method for supplying electricity according to claim 6, characterized in that the semiconductors (13+, 14+, 13-, 14-) of said resistors (11+, 12+, 11-, 12-) are alternately controlled by the interleaving system. fptyUo 4jW) WO 00/43231 PCT / BEOO / OOO'02 2/3 Fig. 2 Fig. 3 f r WO 00/43231 PCT / BEOO / 00002 3/3 s i .. -------------------------------------------------- -------------------------------------------------- -------------------------------------------------- ------------------------- 1 1 1 r i -------------------------------------------------- -------------------------------------------------- ---------- 1 13 * —J I (13-): 1 F 4 1 1 <» 1 · · i l l 14+. 1 (14-) 0 ô T r