DK201770975A1

DK201770975A1 - Protection system with coupled circuit breakers

Info

Publication number: DK201770975A1
Application number: DKPA201770975A
Authority: DK
Inventors: G. Hansen Kenneth
Original assignee: Vestas Wind Systems A/S
Priority date: 2017-12-21
Filing date: 2017-12-21
Publication date: 2018-11-20

Abstract

A power converter system comprising, e.g. for use in a high power wind turbine. First and second power converters CNV1, CNV2 are used to form a combined power electric ouput P_O. First and second circuit breakers CB1, CB2 are connected between power electric outputs of the respective first and second power converters CNV1, CNV2 and the combined power electric output P_O. Fault detectors FD1, FD2, at each circuit breaker CB1, CB2 are used to detect a fault and generate trip signals TS1, TS2 if a fault is detected. The trip signals TS1, TS2 are used to trip both circuit breakers CB1, CB2. Hereby, a rapid tripping is possible of each converter string, and thus preventing a fault, e.g. short-circuit, of propagating through the system. Hereby, a high degree of protection of components in case of a local fault can be obtained. E.g. the trip signals can be sent as digital signals between circuit breaker modules each with digital I/O.

Description

(¹⁹) DANMARK (¹°) DK 2017 70975 A1

(12)

PATENTANSØGNING

Patent- og Varemærkestyrelsen

Int.CI.: H02H 7/12 (2006.01) F03D 80/80 (2016.01) H02J 3/38 (2006.01)

Ansøgningsnummer: PA 2017 70975

Indleveringsdato: 2017-12-21

Løbedag: 2017-12-21

Aim. tilgængelig: 2018-11-19

Publiceringsdato: 2018-11-20

Ansøger:

VESTAS WIND SYSTEMS A/S, Hedeager 42, 8200 Århus N, Danmark

Opfinder:

Kenneth G. Hansen, Charlottenlundvej 39, 8620 Kjellerup, Danmark

Fuldmægtig:

Vestas Wind Systems A/S Patents Department, Hedeager 42, 8200 Århus N, Danmark

Titel: PROTECTION SYSTEM WITH COUPLED CIRCUIT BREAKERS

Fremdragne publikationer:

US 6501628 B1 EP 0330851 A2 WO 2017198268 A1

Sammendrag:

Fortsættes...

DK 2017 70975 A1

CNV1

DK 2017 70975 A1 i

PROTECTION SYSTEM WITH COUPLED CIRCUIT BREAKERS

FIELD OF THE INVENTION

The present invention relates to the field of power converters, more specifically for protection of power converters e.g. for power conversion of electric power generated in wind turbines.

BACKGROUND OF THE INVENTION

In a wind turbine, e.g. with an electric power output of several MW, a parallel connection of several power converters can be advantageous. However, with a high power output, short-circuit protection requires a large and expensive circuit breaker, since such circuit breaker has to handle the total current of the parallel converters.

One result of such design is that it is not possible to protect the single converter strings, as the minimum fault current set for the total current can be close to common load, and thus not detectable by the fault detector of the circuit breaker. Thus, a short-circuit in one converter string may rapidly evolve and cause damage on the entire converter system, before the maximum current for the fault detector reacts and trips the circuit breaker.

SUMMARY OF THE INVENTION

Thus, according to the above description, it is an object of the present invention to provide a power converter system with an effective degree of protection of the components of the system in case of a fault (e.g. short-circuit). Especially, the system should be suitable for a wind turbine.

In a first aspect, the invention provides a power converter system comprising

- first and second power converters,

- a combined power electric ouput formed by a combined connection of power electric outputs of the first and second power converters,

DK 2017 70975 A1

- first and second circuit breakers connected between a power electric output of the respective first and second power converters and the combined power electric output,

- a first fault detector arranged to detect a fault, and to generate a first trip signal accordingly, so as to cause the first circuit breaker to break electric connection between the power output of the first power converter and the combined power electric output,

- a second fault detector arranged to detect a fault, and to generate a second trip signal accordingly, so as to cause the second circuit breaker to break electric connection between the power output of the second power converter and the combined power electric output, and

- a connection mechanism arranged to transmit the first trip signal to the second circuit breaker and to transmit the second trip signal to the first circuit breaker, so as to allow the first and second circuit breakers to mutually break connection of power outputs of the first and second power converters.

Such system is advantageous, since it allows a plurality of parallel coupled power converters to be effectively protected in case of faults in one single converter string due to the mutual coupling of the circuit breakers. E.g. in case of a total clearing time of a relay based circuit breaker of 75 ms, about 40 ms can be saved for clearing of the second circuit breaker with the mutual trip signal coupling proposed. Such 40 ms can be significant time to save components which would otherwise be damaged if the two circuit breakers had to sequentially detect a fault and trip subsequently. It has been found that a tripping delay of only 10 ms is possible with such mutual coupling.

Further, the trip signals can be used to trip a circuit breaker at an input of the converts, e.g. in case of a power electric input from a permanent magnet generator which requires such circuit breaker, e.g. in a wind turbine.

Even further, the trip signals can be provided to an overall controller which can act accordingly, e.g. a wind turbine controller.

The invention can be exploited using existing relay-based circuit breaker components. E.g. processor controlled programmable circuit breaker modules with

DK 2017 70975 A1 built-in fault detectors (current detectors) can be used. Such modules are capable of generating a suitable trip signal in a digital format and output it as an electric digital output signal, and with a simple wire connection to other circuit breaker modules, mutual tripping is possible.

The invention does not require any mechanical interlock between the circuit breakers, and thus the circuit breakers can be located near other components of each converter string.

In the following, preferred embodiments and features ofthe gatedriver circuit will be described.

The first and second circuit breakers may comprise respective relays for breaking power electric connection.

The first and second fault detectors may comprise respective current sensors arranged to sense a current, and to detect a fault in case the sensed current exceeds a preset current limit, e.g. a preset current limit of more than 1 kA, such as 2-10 kA.

Especially, the first fault detector and the first circuit breaker may be arranged within a first housing, and wherein the second fault detector and the second circuit breaker may be arranged within a second housing separate from the first housing. Especially, existing processor based relay modules can be used, which are compact and low cost standard components which has a digital I/O interface, thus being suitable for generating and receiving a trip signal in a digital format.

A first processor may be arranged to control operation of the first fault detector and the first circuit breaker, and a second processor may be arranged to control operation of the second fault detector and the second circuit breaker.

The the connection mechanism may comprise a digital connection module for transmitting the first and second trip signals to the respective second and first circuit breakers represented in a digital format.

DK 2017 70975 A1

The connection mechanism may comprises at least one electrical conductor, preferably electrically insulated wires, such as copper wires or wires of other electrically conductive materials, to transmit the first and second trip signals as respective electric signals, either as analog or digital electric signals. Alternatively, or additionally, the connection mechanism may comprise a wireless transmitter and receiver for transmitting the first and second trip signals in a wireless format. The wireless format may be optical or radio frequency signals or the like.

The power converter system according to any of the preceding claims, comprises a third power converter, and wherein the combined power electric ouput is formed by a combined connection of power outputs of all of the first, second and third power converters.

Each of the first and second power converters may comprise a plurality of power electronic switches and an electric gatedriver circuit for controlling the plurality of power electronic switches.

The first and second power converters each comprising a plurality of power electronic switches controlled and an electric gatedriver circuit according to the first aspect for controlling the plurality of power electronic switches. Especially, the gatedriver circuit is arranged to generate the electric control signal output to control the plurality of power electronic switches at a switching frequency of below 10 kHz, e.g. 1-10 kHz. The power converters may especially comprise an insulated gate bipolar transistor (IGBT) module, wherein the gatedriver circuit is arranged to control switching of the IGBT module. Alernatively, or additionally, the power electronic switches may include one or more of: MOSFET, GTO, IGCT, and/or comprises power electronic switches based on silicon carbide (SiC) technologies. Especially, the power converter system may be dimensioned to convert electric power of at least 1 MW, such as 2-10 MW or more.

In a second aspect, the invention provides a windt urbine comprising power converter system according to the first aspect.

Especially, the first and second trip signals may be provided to a wind turbine controller, e.g. SCADA controller, configured to control the wind turbine in

DK 2017 70975 A1 response to the first and second trip signals. This allows for improved control of the wind turbine, dince a local detection of a fault, e.g. a local short-circuit, is communicated in a fast manner to the overall wind turbine controller. Especially, the wind turbine controller may be part of the connection mechanism, where the plurality of trip signals from distributed circuit breakers are sent to the wind turbine controller, which then distributes trip signals to all circuit breakers involved in response to receiving a trip signal from one circuit breaker.

In an embodiment, the wind turbine comprises a

- a permanent magnet (PM) type electric generator for generating electric power to be converted by the power converter system, and

- a third circuit breaker connected so as to form a breakable power electric connection between the electric generator and a power electric input of the power converter system, wherein the third circuit breaker is connected via a connection mechanism to receive at least one of the first and second trip signals, so as to allow the third circuit breaker to break connection between the electric generator and the power converter system in response to at least one of the first and second trip signals. Hereby, it is possible to break connection between converters and the PM generator, which is required, in case a fault occurs.

It is to be understood that the invention is applicable also in system with more than three power converters in parallel, each with its dedicated circuit breaker and fault detector.

In a third aspect, the invention provides a method for protecting a power converter system with a combined power electric ouput formed by a combined connection of power electric outputs of first and second power converters, the method comprising

- generating a first trip signal in response to a detected fault,

- causing a first circuit breaker to break electric connection between a power output of the first power converter and the combined power electric output in response to the first trip signal,

- transmitting the first trip signal to a second circuit breaker, and

DK 2017 70975 A1

- causing the second circuit breaker to break electric connection between a power output of the second power converter and the combined power electric output in response to the first trip signal.

It is to be understood that the same advantages and preferred embodiments and features apply for the second and third apsects, as described for the first aspect, and the aspects may be mixed in any way.

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be described in more detail with regard to the accompanying figures of which

Fig. 1 illustrates a wind turbine, in which the power converter system of the invention is advantageous,

Fig. 2 illustrates a power converter embodiment,

Fig. 3 (Illustrates another power converter embodiment,and

Fig. 4 illustrates steps of a method embodiment.

The figures illustrate specific ways of implementing the present invention and are not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

DETAILED DESCRIPTION OF THE INVENTION

Fig. 1 illustrates a wind turbine with three rotor blades for driving an electric generator located inside the nacelle on top of a tower. Typically, the power converter system in a wind turbine can be placed up-tower or down tower. The full scale converter typically comprises a power stack for AC/DC conversion and a power stack for DC/AC conversion. Furthermore the converter system comprises reactors, filter capacitors, breakers, busbars and other converter related systems. The power converter system according to the invention is advantageous for wind turbines, e.g. wind turbines capable of generating high electric power such as more than 1 MW. However, it is to be understood that the invention may be used

DK 2017 70975 A1 as well in other power electric applications, especially for applications ranging from such as 1 kW and upwards.

Especially, the wind turbine may comprise an electric power generator arranged to generate an electric power of at least 1 MW, such as 2-10 MW, or more. In such MW wind turbines, the invention is advantageous, since parallel converters can be used to provide a high total output power, while using circuit breakers for each of the parallel connected converters allow for the use of rather compact circuit breakers with a limited maximum current rating, and still with the mutual trip signal coupling, it is possible to protect all components in case of a short-circuit or other faults, due to the rapid circuit breaker tripping.

In wind turbine applications, it is advantagesous for the power converter control system to get reliable status feedback from the involved circuit breakers. The status feedback is often an auxiliary relay indicating if the main contacts are open or closed. If the circuit breaker is opened by the circuit breaker protection relay due to an over current/short-circuit, where the circuit breaker protection relay have sent trip signal to the circuit breaker, an additional feedback auxiliary relay can provide that feedback to the converter control system. The trip feedback is advantageous, to provide the correct cause to a supervisory control and data acquisition (SCADA) system, and to avoid a reclose of circuit breakers without inspection. The benefit is that the solution is not relying on bus communication, but can be implemented on all circuit breakers with option for separate trip feedback relay.

Fig. 2 shows a power converter system embodiment where two power converters CNV1, CNV2 are connected in parallel for converting a power electrinc input P_I to a combined power electric ouput P_O. First and second circuit breakers CB1, CB2 are connected between a power electric output of the respective first and second power converters CNV1, CNV2 and the combined power electric output P_O.

A first fault detector FD1 is arranged to detect a fault, e.g. to detect if a current at the output of the first converter exceeds a preset current limit. If so, it generates a first trip signal TS1 accordingly, so as to cause the first circuit breaker CB1 to

DK 2017 70975 A1 break electric connection between the power output of the first power converter CNV1 and the combined power electric output P_O.

Likewise, a second fault detector FD2 is arranged to detect a fault, e.g. to detect if a current at the output of the first converter exceeds a preset current limit. If so, it generates a second trip signal TS2 accordingly, so as to cause the second circuit breaker CB2 to break electric connection between the power output of the second power converter CNV2 and the combined power electric output P_O.

A connection mechanism CM, e.g. electrical wire(s), is arranged to transmit the first trip signal TS1 to the second circuit breaker CB2 and to transmit the second trip signal TS2 to the first circuit breaker CB1. This allows that the first and second circuit breakers CB1, CB2 mutually break connection of power outputs of the two power converters CNV1, CNV2.

The first and second circuit breakers CB1, CB2 are preferably relay modules with a built-in fault detector FDI, FD2 and with a processor controlling operation as well as a digital I/O interface. Such module allows for programming of the fault detector current as well as programming of the transmission of an external trip signal as a digital signal along with tripping of the internal relay. This allows a simple connection mechanism in the form of an electric wire with one ore more conductors. For wind turbine applications, the circuit breakers CB1, CB2 can preferably handle at least 1 kA, such as 2-10 kA.

The total clearing time for a relay includes: 1) protection relay delay, 2) mechanical opening time, and 3) contact arc destingush. Typically a total of 75 ms. With the mutual use of the trip signal, it is possible to trip relays of all converter strings with only 10 ms delay after a fault has been detected in one converter string. Hereby, a short-circuit fault can be prevented from propagating through the entire converter system.

The function to electrical interlock the trip of bircuit breakers for parallel converters can be done in at least the following two ways:

DK 2017 70975 A1

1) The circuit breaker trip feedback signal can be used to trigger a relay which proactive opens the other circuit breakers as well.

2) If the circuit breaker protection relay contains programmable I/O, it could be possible to send the opening signal by I/O instead of external relay. At the same time the circuit breaker relay powers the trip coil of the circuit breaker, it could send trip output, which is then read by the other circuit breaker's inputs. It will limit the delay from first circuit breaker opens, to other circuit breakers are opened, as the parallel circuit breakers are not waiting for first circuit breaker to fully open, as the signal transfer starts from first fault detector decides to send trip signal.

Both solutions provide the advantage of preventing a fault from propagating to the other parallel systems. It is to be understood that more than two converters can be arranged in parallel, each converter having a controllable circuit breaker for protection.

The power converters CNV1, CNV2 may be DC-AC or AC-DC-AC converters. It is to be understood that the power converters CNV1, CNV2 can be formed by various technologies. In preferred versions, the converts CNV1, CNV2 comprise a control circuit for controlling switching of a plurality of power electronic switches, e.g. IGBTs, such as operating at a switching frequency of 1 kHz to 10 kHz.

Fig. 3 illustrates an embodiment with the same components as mentioned in connection with Fig. 2, but where the power input P_I is provided by a permanent magnet (PM) power generator PG, as in a wind turbine. Here, a third circuit breaker CB3 is connected so as to form a breakable power electric connection between the electric generator PG and a power electric input P_I of the power converter system. This is a normal requirement for fault protection in case of a PM power generator PG.

The third circuit breaker CB3 is connected via a connection mechanism to receive at least one of the first and second trip signals TSI, TS2, so as to allow the third circuit breaker CB3 to break connection between the electric generator PG and the

DK 2017 70975 A1 power converter system in response to at least one of the first and second trip signals TSI, TS2.

Hereby, it is possible to quickly break connection to the PM power generator PG, in case a fault is detected in a power converter string, and thus possible damage of additional components can be avoided.

Fig. 4 illustrates steps of an embodiment of a method for protecting a power converter system with a combined power electric ouput P_O formed by a combined connection of power electric outputs of first and second power converters CNV1, CNV2. The method comprises generating G_TS1 a first trip signal TS1 in response to a detected fault. Next, causing C_CB1 a first circuit breaker CB1 to break electric connection between a power output of the first power converter CNV1 and the combined power electric output P_O in response to the first trip signal TS1. At the same time, transmitting (T_TS1) the first trip signal TS1 to a second circuit breaker CB2, and causing C_CB2 the second circuit breaker CB2 to break electric connection between a power output of the second power converter CNV2 and the combined power electric output P_O in response to the first trip signal TS1.

To sum up: the invention provides a power converter system comprising, e.g. for use in a high power wind turbine. First and second power converters CNV1, CNV2 are used to form a combined power electric ouput P_O. First and second circuit breakers CB1, CB2 are connected between power electric outputs of the respective first and second power converters CNV1, CNV2 and the combined power electric output P_O. Fault detectors FDI, FD2, at each circuit breaker CB1, CB2 are used to detect a fault and generate trip signals TSI, TS2 if a fault is detected. The trip signals TSI, TS2 are used to trip both circuit breakers CB1, CB2. Hereby, a rapid tripping is possible of each converter string, and thus preventing a fault, e.g. short-circuit, of propagating through the system. Hereby, a high degree of protection of components in case of a local fault can be obtained. E.g. the trip signals can be sent as digital signals between circuit breaker modules each with digital I/O.

DK 2017 70975 A1

Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is to be interpreted in the light of the accompanying claim set. In the context of the claims, the terms including or includes do not exclude other possible elements or steps. Also, the mentioning of references such as a or an etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

DK 2017 70975 A1

Claims

1. A power converter system comprising

- first and second power converters (CNV1, CNV2),

- a combined power electric ouput (P_O) formed by a combined connection of power electric outputs of the first and second power converters (CNV1, CNV2),

- first and second circuit breakers (CB1, CB2) connected between power electric outputs of the respective first and second power converters (CNV1, CNV2) and the combined power electric output (P_O),

- a first fault detector (FD1) arranged to detect a fault, and to generate a first trip signal (TS1) accordingly, so as to cause the first circuit breaker (CB1) to break electric connection between the power output of the first power converter (CNV1) and the combined power electric output (P_O),

- a second fault detector (FD2) arranged to detect a fault, and to generate a second trip signal (TS2) accordingly, so as to cause the second circuit breaker (CB2) to break electric connection between the power output of the second power converter (CNV2) and the combined power electric output (P_O), and

- a connection mechanism (CM) arranged to transmit the first trip signal (TS1) to the second circuit breaker (CB2) and to transmit the second trip signal (TS2) to the first circuit breaker (CB1), so as to allow the first and second circuit breakers (CB1, CB2) to mutually break connection of power outputs of the first and second power converters (CNV1, CNV2).

2. The power converter system according to claim 1, wherein the first and second circuit breakers (CB1, CB2) comprise respective relays for breaking power electric connection.

DK 2017 70975 A1

3. The power converter system according to claim 1 or 2, wherein the connection mechanism (CM) comprises a digital connection module for transmitting the first and second trip signals (TSI, TS2) to the respective second and first circuit breakers (CB2, CB1) represented in a digital format.

4. The power converter system according to any of the preceding claims, wherein the connection mechanism (CM) comprises at least one electrical conductor to transmit the first and second trip signals (TSI, TS2) as respective electric signals.

5. The power converter system according to any of the preceding claims, wherein the connection mechanism (CM) comprises a wireless transmitter and receiver for transmitting the first and second trip signals (TSI, TS2) in a wireless format.

6. The power converter system according to any of the preceding claims, wherein the first and second fault detectors (FDI, FD2) comprise respective current sensors arranged to sense a current, and to detect a fault in case the sensed current exceeds a preset current limit.

7. The power converter system according to any of the preceding claims, wherein said preset current limit is more than 1 kA.

8. The power converter system according to any of the preceding claims, wherein the first fault detector (FD1) and the first circuit breaker (CB1) are arranged within a first housing, and wherein the second fault detector (FD2) and the second circuit breaker (CB2) are arranged within a second housing separate from the first housing.

9. The power converter system according to any of the preceding claims, comprising a first processor arranged to control operation of the first fault detector (FD1) and the first circuit breaker (CB1), and comprising a second processor arranged to control operation of the second fault detector (FD2) and the second circuit breaker (CB2).

10. The power converter system according to any of the preceding claims, comprises a third power converter, and wherein the combined power electric

DK 2017 70975 A1 ouput (P_O) is formed by a combined connection of power outputs of all of the first, second and third power converter (CNV1, CNV2).

11. The power converter system according to any of the preceding claims, wherein each of the first and second power converters (CNV1, CN2) comprise a plurality of power electronic switches and an electric gatedriver circuit for controlling the plurality of power electronic switches.

12. A wind turbine comprising a power converter system according to any of claims 1-11.

13. The wind turbine according to claim 12, wherein the first and second trip signals (TSI, TS2) are provided to a wind turbine controller configured to control the wind turbine in response to the first and second trip signals (TSI, TS2).

14. The wind turbine according to claim 12 or 13, comprising

- a permanent magnet type electric generator (PG) for generating electric power to be converted by the power converter system, and

- a third circuit breaker (CB3) connected so as to form a breakable power electric connection between the electric generator (PG) and a power electric input (P_I) of the power converter system, wherein the third circuit breaker (CB3) is connected via a connection mechanism to receive at least one of the first and second trip signals (TSI, TS2), so as to allow the third circuit breaker (CB3) to break connection between the electric generator (PG) and the power converter system in response to at least one of the first and second trip signals (TSI, TS2).

15. A method for protecting a power converter system with a combined power electric ouput (P_O) formed by a combined connection of power electric outputs of first and second power converters (CNV1, CNV2), the method comprising

DK 2017 70975 A1

- generating (G_TS1) a first trip signal (TS1) in response to a detected fault,

- causing (C_CB1) a first circuit breaker (CB1) to break electric connection

5 between a power output of the first power converter (CNV1) and the combined power electric output (P_O) in response to the first trip signal (TS1),

- transmitting (T_TS1) the first trip signal (TS1) to a second circuit breaker

10 (CB2), and

- causing (C_CB2) the second circuit breaker (CB2) to break electric connection between a power output of the second power converter (CNV2) and the combined power electric output (P_O) in response to the first trip

15 signal (TS1).

DK 2017 70975 A1