CN1698253A - Structure and method for protecting a converter device - Google Patents

Abstract

A protection structure for a converter device (INU), the converter device comprising a plurality of controllable switches (V1 to V6), the protection structure comprising a protection circuit (2) coupled to the AC voltage side of the converter device (INU), the protection circuit comprising at least one protection switch (V11), the protection switch being configured to short-circuit the AC voltage side of the converter device (INU), wherein in a predetermined fault condition, the protection structure is configured to close the protection switch (V11) and thereby short-circuit the AC voltage side of the converter device (INU). After the fault condition is eliminated, the protection structure is configured to short-circuit the AC voltage side of the converter device (INU) via the controllable switches (V2, V4, V6) to increase the commutation of the protection switch (V11).

Description

Structure and method for protecting a converter device

technical field

The invention relates to the protection of converter devices in motor drives against overvoltages and overcurrents.

Background technique

Converters are used in various generator and motor drives. One such motor drive including a converter is a double feedback slip-ring generator structure, the rotor circuit of which comprises two converters with a DC voltage intermediate circuit between them. One of these converters is located between the DC voltage intermediate circuit and the rotor, and the other converter is electrically located between the DC voltage intermediate circuit and the network to be supplied.

Such double feedback slip ring generator structures with specific rated speeds are usually configured to operate within a specific speed range with upper and lower limits according to the selected stator and rotor transformation coefficients. The speed range of a double feedback slip ring generator structure with a rated speed of 1500 1/min can be, for example, 1000 to 2000 1/min. When the generator rotates at a speed less than the rated speed, some of the power fed back through the stator is fed back to the rotor via slip rings of the converter and generator. Likewise, when the generator rotates at a speed greater than the rated speed, power is fed back from the rotor via the rotor's slip rings and the converter to the network powered by the generator.

When the speed range of the generator structure complies with the above values, i.e. the structure is configured to work in the speed range, where this range deviates from one-third of the rated speed of the generator, the size of these two converters of the rotor circuit may be only One-third of the generator power. This saves investment costs, but the relatively low power handling capability of the converter has to be taken into account when designing the protection of the generator structure.

During a network failure, the voltage of the DC voltage intermediate circuit may rise high enough due to the transformation factor of the power generation to cause damage to the converter in the rotor circuit. It is known to protect the converter in the rotor circuit by a protective circuit comprising a thyristor so that in the event of a fault the rotor circuit is short-circuited between the rotor and the converter via the thyristor. With the triggering of the thyristor, the switch of the converter is opened so that the current flow of the converter is terminated. This makes it possible to protect the converter of the rotor circuit from overvoltage and to protect the zero diode of the converter from overcurrent.

There are various problems depending on the type and performance of the motor drive whose converter is protected by the protection circuit implemented by the thyristor as described above. In all cases, the basic problem is to protect the commutation of the thyristors. For example, in the case of the double feedback slip ring generator configuration described above, there is a problem that normal operation of the generator configuration cannot be resumed after a fault unless the generator is first de-energized. The prerequisite for keeping the generator in a no-current state depends on protecting the thyristors from reliable commutation.

Contents of the invention

It is an object of the present invention to provide a protection structure for a converter device such that the above-mentioned problems can be solved. This object of the invention is achieved by a protective structure for a converter device, the features of which are disclosed in the independent claims. Preferred embodiments of the invention are disclosed in the dependent claims.

The basic idea of the invention is to increase the commutation of the protective switch in the protective circuit of the converter device by short-circuiting the AC voltage side of the converter device with a controllable switch belonging to the converter device.

An advantage of the protective structure of the present invention is that normal operation of the motor structure can be continued substantially immediately after a fault condition.

A further object of the invention is to provide a method of using a protective structure for a converter device.

Description of drawings

Describe the present invention in detail now in conjunction with preferred embodiment and with reference to accompanying drawing, in the accompanying drawing:

FIG. 1 shows a protection structure for a converter device according to an embodiment of the present invention;

Figure 2 shows a wind drive comprising the protective structure of Figure 1; and

3 to 8 show the currents and voltages in the event of a fault in the wind drive of FIG. 2 .

Detailed ways

Figure 1 shows a protection structure for a rotor circuit of a double feedback slip ring generator according to an embodiment of the invention, the protection structure comprising a rotor side converter device INU, a du/dt filter 8 coupled to phases L1 to L3 , and protection circuit 2. For the sake of simplicity, the components configured to measure the electrical quantity, process the measurement results and control the switches are not shown in the figure.

The rotor-side converter device INU has a DC voltage side and an AC voltage side. The direct voltage side is electrically coupled to the direct voltage intermediate circuit 3 . The AC voltage side is electrically coupled to the rotor of the generator. The rotor-side converter device INU comprises means for rectifying the three-phase voltage of the rotor and for feeding it to the DC voltage intermediate circuit 3, and for inverting the DC voltage of the DC voltage intermediate circuit 3 and for feeding it to The device that feeds the rotor. In this way, the rotor-side converter device INU is configured to feed power both to the rotor and to the network supplied by the generator.

In FIG. 1 , the protection circuit 2 is coupled between the rotor-side converter device INU and the du/dt filter 8 . A du/dt filter 8 can also be coupled to the AC voltage-side output of the rotor-side converter device INU in order to generate a du/dt filter between the converter device INU and the protective circuit. Likewise, the du/dt filter can be split into two parts and the protection circuit 2 is coupled between the two parts. Sometimes, such a du/dt filter 8 can also be completely omitted from the structure.

The rotor-side converter device INU comprises six controllable switches V1 to V6 configured to modulate an alternating voltage derived from the direct voltage of the direct voltage intermediate circuit 3 . The switches V1 to V6 can be, for example, transistors or other corresponding semiconductor switches.

The rotor-side converter arrangement INU further comprises six null diodes D1 to D6, each coupled in parallel with a corresponding switch V1 to V6. Null diodes D1 to D6 are coupled in such a way that they rectify the current flowing from the rotor to the direct voltage intermediate circuit 3 . In one embodiment, zero diodes D1 to D6 are integrated into corresponding controllable switches V1 to V6. For example, IGBTs contain this structure.

The protection circuit 2 with the structure shown in FIG. 1 includes a three-phase rectifier bridge realized by diodes. The protection switch V11 and the auxiliary commutation device 10 are coupled in series between the positive pole and the negative pole of the rectifier bridge, wherein the auxiliary commutation device 10 is configured to improve the commutation of the protection switch V11 . The auxiliary commutation device 10 includes a plurality of diodes V12 to V(n) coupled in series, and a capacitor C coupled in parallel with the plurality of diodes. The protection switch V11 can be, for example, a thyristor.

FIG. 2 shows a wind drive including the protective structure shown in FIG. 1 . The wind drive shown in Figure 2 uses an asynchronous generator 1 equipped with slip rings. In addition to the protective circuit 2 , the rotor-side converter INU and the direct voltage intermediate circuit 3 , the rotor circuit of the asynchronous generator 1 also includes a network converter ISU. The rotor circuit is connected via a switch 4 of the rotor circuit, a power transformer 5 and a medium voltage switchgear 6 to the grid to be supplied. The stator circuit of the asynchronous generator 1 is connected to the grid to be supplied via the main switch 7 when the main switch 7 is located at the point where the stator of the generator 1 and the stator and rotor circuits converge on power Between the points before transformer 5.

When the protection structure of the rotor circuit detects a network failure meeting the predetermined conditions, the protection structure opens the switches V1 to V6 and controls the protection switch V11 to close. A network fault can be defined, for example, as a situation in which the rotor current or the voltage of the DC intermediate circuit exceeds a predetermined limit value. Closing the protection switch V11 short-circuits the rotor circuit, so that the short-circuit current from the rotor flows through the protection switch V11 of the protection circuit 2 .

In the case of the structure shown in FIG. 2 , a network fault meeting the predetermined condition may be, for example, a voltage dip of the network to be powered. Without protective measures, voltage dips in the network to be supplied can lead to dangerous sudden increases in the rotor and stator currents as well as in the voltage of the direct voltage intermediate circuit 3 .

When the protection structure detects that the network fault has ended, it closes the switches V2, V4 and V6, so that the short-circuit current from the rotor is diverted from the protection circuit 2 to the rotor-side converter device, so that the short-circuit current starts to flow through the DC voltage intermediate circuit 3 The negative bus Udc-. Alternatively, by closing the switches V1 , V3 and V5 the short-circuit current from the rotor can be diverted from the protection circuit 2 to the rotor-side converter device, so that the short-circuit current starts flowing through the positive busbar Udc+ of the DC voltage intermediate circuit 3 . The diversion of the short-circuit current from the rotor to the rotor-side converter device depends on the combined threshold voltage of the diode bridge, protection switch V11 and diode V12 to V(n) in the protection circuit 2 being higher than the rotor-side converter through which the short-circuit current flows Threshold voltage of the elements in the device INU. In order to enable the protection switch V11 to be commutated, it is desirable to divert the short-circuit current from the rotor to a position away from the protection circuit 2 .

Capacitor C of protection circuit 2 coupled in parallel with diodes V12 to V(n) and charged when a short circuit current flows in protection circuit 2 assists protection switch V11 in commutation.

When the short-circuit current has been transferred from the protection circuit 2 to the rotor-side converter device, that is, the short-circuit current has started to flow through the closed switches V2, V4 and V6 (or V1, V3 and V5), and the protection switch V11 has completed commutation, Modulation can be restarted by using switches V1 to V6.

The auxiliary reversing device 10 can also be realized in other ways than that shown in FIG. 1 . For example, one or more resistors in series with protection switch V11 may be added. Diodes V12 to V(n) can be replaced by other elements with suitable threshold voltages. The auxiliary commutation device may be at least partially integrated into the protection switch V11, and the protection switch V11 may be configured to be turned off according to the control signal. Therefore, the protection switch V11 can be, for example, an IGBT or a GTO. The protection circuit 2 may include a phase-specific protection switch V11, so that the protection circuit 2 does not require a rectifier bridge. The auxiliary commutation device 10 may further include a forced commutation circuit coupled in parallel with the protection switch V11. Such forced commutation circuits are well known in the art, so their structure will not be discussed here.

In the case of the structure shown in Figure 1, and when the operating conditions are such that the fault condition has ended and the switches V2, V4 and V6 are closed in order to divert the short-circuit current from the rotor to flow through the switches, for example, by measuring The currents flowing through the switches V2, V4 and V6 and the rate of change of these currents effect the commutation of the protection switch V11. The details of the commutation operation of the protective switch V11, such as the duration of the commutation operation, depend on the type of the protective switch V11 and therefore must be taken into account when selecting the control parameters of the protective structure.

Normal operation of the rotor-side converter INU starting from a situation in which the protection switch V11 of the protection circuit 2 has commutated and the three-phase sides of the converter INU have been short-circuited through the controllable switches V2, V4 and V6 may be problematic. If the modulation continues normally, the rotor and stator currents of the generator 1 may remain high and difficult to control for long periods of time. Abnormal operating conditions may also occur without further action.

The aforementioned problems in controlling the rotor and stator currents can be solved by opening the rotor circuit, after which the generator 1 is seen from the network to be supplied as if it were an open transformer or choke. Consequently, the current of the generator stator rapidly drops to a level substantially corresponding to its magnetizing current. Normal operation of the rotor circuit can then be safely started.

In the configuration shown in Fig. 2, the current of the rotor circuit can be measured and used to determine the moment at which normal modulation can be started by switches V1 to V6 of the rotor-side converter INU. For example in the case of a voltage dip in the network to be supplied, which causes the protective switch V11 to close, when the controllable switches V1 to V6 are opened after the commutation of the protective switch V11, it is possible to measure the current of the rotor circuit by to estimate the probability of starting normal modulation. Such a measurement can be performed, for example, within the rotor-side converter INU. When the current burst is no longer detected in the rotor circuit, it is safe to start normal modulation.

The rotor circuit can be opened, for example, by opening the controllable switches V1 to V6 of the converter INU. If the structure shown in FIG. 2 is provided with a further switch between the rotor of the generator 1 and the rotor-side converter INU, the rotor circuit can be opened via this further switch.

The stator circuit of the wind-driven generator 1 shown in FIG. 2 can remain coupled to the network to be supplied throughout the entire network failure (eg voltage dip). If the previously mentioned opening action of the rotor circuit for smoothing the rotor and stator currents is performed by opening the controllable switches V1 to V6 of the rotor-side converter INU, the network converter ISU is coupled to the On the stator circuit and on the network to be powered, so that the network converter ISU maintains the voltage of the DC voltage intermediate circuit 3 during a network failure.

When the protection structure shown in FIG. 1 receives information indicating that there may be a fault in the network to be powered, where a short circuit of the protection circuit 2 is required at this time, it is possible to first open the switches V1 to V6 and wait for a period before closing the protection switch V11. predetermined time period. During this time period, if current and/or voltage information is received indicating that the fault requiring the protective switch V11 to be closed has ended, operation continues in the normal manner.

In the above description, the opening of the controllable switches V1 to V6 means that the purpose is to open these switches by control. Thus, depending on the type of the controllable switches V1 to V6, they are for example not further activated, and if the controllable switches are configured to cut themselves off according to the control of the passing current, this opening consists in feeding an opening pulse to the switches. For example, in case a high current flows through the controllable switches V1 to V6 of the rotor-side converter INU in a fault situation, the aforementioned control procedure does not need to successfully end the current flow through the switches V1 to V6. Thus, using what was used in the above description, opening the switches V1 to V6 does not necessarily cut off the current through them, but the protection switch V11 also needs to be closed. As such, the situation is similar to a situation where a mechanical switch has been opened but an arc has occurred in it.

The simulation of the motor structure continues even when the switches V1 to V6 have been opened. In the generator configuration shown in FIG. 2 , the control device always knows, for example, the stator and rotor currents, the voltage of the network to be fed, the position of the shaft and the rotational speed of the generator. It is advantageous to continue the simulation when estimating a safe moment to continue the modulation.

3 to 8 show the current and voltage situation in the wind drive shown in FIG. 2 when the protective structure of the converter device is used in the above-described manner when the voltage of the network to be supplied drops by 65%. The values of current and voltage were measured at 20 microsecond intervals during a time period of -0.04000 seconds to 0.28764 seconds. Figures 3 to 8 show the following quantities:

Figure 3 Uuv, rot = phase voltage U-V of the rotor side converter (INU)

Figure 4 Iu, rot = U-phase current of the rotor-side converter (INU)

Figure 5 Udc, crowbar = the voltage of the rectifier bridge in the protection circuit 2

Figure 6 Idc, crowbar = current of protection switch V11 in protection circuit 2

Figure 7 Uuw, grid = phase voltage U-W of the network to be powered

Figure 8 Iu, grid = U-phase current of the network to be powered

Although the examples shown herein relate to the protection of converters of rotor circuits in double feedback slip ring generators, the protection structure of the present invention can also be used to protect converters of other types of motor structures. The protection structure of the invention is suitable for protecting converters driven by asynchronous and synchronous motors, and such drives may be generator-driven or motor-driven. It is obvious to a person skilled in the art that the basic idea of the invention can be implemented in many different ways. The invention and its embodiments are therefore not limited to the examples described above but may vary within the scope of the claims.

Claims (14)

1. protection structure that is used for converter apparatus (INU); this converter apparatus has the DC voltage side that is coupled to dc voltage intermediate circuit (3); with the alternating voltage side; and this converter apparatus (INU) comprises that the direct voltage that is used for dc voltage intermediate circuit (3) carries out inversion and is used for it is fed to the device of alternating voltage side; this inverter comprises a plurality of gate-controlled switches (V1 is to V6); this protection structure comprises the protective circuit (2) of the alternating voltage side that is coupled to converter apparatus (INU); this protective circuit comprises that at least one is configured in order to the turn round protection switch (V11) of alternating voltage side of parallel operation device (INU) of short circuit; wherein under predetermined failure condition; this protection structural arrangements becomes closed protection switch (V11); and the therefore short circuit alternating voltage side of turning round parallel operation device (INU); it is characterized in that; after failure condition finished, the protection structural arrangements became by gate-controlled switch (V2; V4; V6) short circuit is turned round the alternating voltage side of parallel operation device (INU) to improve the commutation of protection switch (V11).

2. protection structure as claimed in claim 1; it is characterized in that; under predetermined failure condition; this structural arrangements becomes at closed protection switch (V11) before; open a plurality of gate-controlled switches (V1 is to V6) of DC-to-AC converter in the converter apparatus (INU), and keep gate-controlled switch (V1 is to V6) to open till failure condition finishes.

3. protection structure as claimed in claim 1 or 2 is characterized in that, after protection switch (V11) commutation, this structural arrangements becomes to open the gate-controlled switch (V1 is to V6) of converter apparatus (INU), and keeps them to open till can beginning modulation safely.

4. any one described protection structure in the claim as described above is characterized in that protective circuit (2) comprises auxiliary commutation means (10), and this auxiliary commutation means (10) is configured in order to improve the commutation of protection switch (V11).

5. protection structure as claimed in claim 4 is characterized in that, auxiliary commutation means (10) comprise with a plurality of diodes (V12, V (n)) of protection switch (V11) series coupled and with the capacitor (C) of these a plurality of diode parallel coupled.

6. any one described protection structure in the claim as described above; it is characterized in that converter apparatus (INU) comprises that further the alternating voltage that is used for the alternating voltage side carries out rectification and it is fed to the device (D1 is to D6) of dc voltage intermediate circuit (3).

7. any one described protection structure in the claim as described above; it is characterized in that; when failure condition finishes and protection switch (V11) when commutating; this structural arrangements becomes to turn back to normal operating conditions, wherein in the control transformation apparatus (INU) a plurality of gate-controlled switches (V1 is to V6) of DC-to-AC converter so that the direct voltage of dc voltage intermediate circuit (3) is carried out inversion.

8. any one described protection structure in the claim as described above is characterized in that this structural arrangements becomes the rotor circuits of protection two feedback slip ring generators (1).

9. a use is used for the method for the protection structure of converter apparatus; this converter apparatus has the DC voltage side that is coupled to dc voltage intermediate circuit (3); with the alternating voltage side; and this converter apparatus (INU) comprises that the direct voltage that is used for dc voltage intermediate circuit (3) carries out inversion and is used for it is fed to the device of alternating voltage side; this inverter comprises a plurality of gate-controlled switches (V1 is to V6); this protection structure comprises the protective circuit (2) of the alternating voltage side that is coupled to converter apparatus (INU); this protective circuit comprises that at least one is configured in order to the turn round protection switch (V11) of alternating voltage side of parallel operation device (INU) of short circuit; this method is included in closed protection switch (V11) under the predetermined failure condition and the therefore short circuit step of alternating voltage side of turning round parallel operation device (INU); it is characterized in that; after this method further is included in the failure condition end, by gate-controlled switch (V2; V4; V6) short circuit is turned round the alternating voltage side of parallel operation device (INU) with the step of the commutation that improves protection switch (V11).

10. method as claimed in claim 9; it is characterized in that; under predetermined failure condition; at closed protection switch (V11) before; open a plurality of gate-controlled switches (V1 is to V6) of DC-to-AC converter in the converter apparatus (INU), and keep gate-controlled switch (V1 is to V6) to open till failure condition finishes.

11., it is characterized in that after protection switch (V11) had commutated, this method comprised by opening current circuit under the converter apparatus so that the currentless step of converter apparatus (INU) as claim 9 or 10 described methods.

12. method as claimed in claim 11 is characterized in that, carries out opening of current circuit by the gate-controlled switch (V1 is to V6) of opening converter apparatus.

13., it is characterized in that after protection switch (V11) commutation, the current circuit under the converter apparatus (INU) remains to be opened till can beginning modulation safely as claim 11 or 12 described methods.

14. method as claimed in claim 13; it is characterized in that; converter apparatus (INU) is the converter apparatus of two feedback slip ring generator (1) rotor-side; and after protection switch (V11) commutation, the current circuit under the converter apparatus remains to be opened till the electric current of generator (1) stator drops to the level that corresponds essentially to its magnetizing current.

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