Patent Description:
During commissioning of a wind turbine assembly, there might be excessive moisture in electrical components of the wind turbine assembly. The excessive moisture can cause breakthroughs in the electrical components, thereby causing damages in the electrical components. Consequently, it is important to remove excessive moisture from electrical components of a wind turbine assembly before starting up the wind turbine assembly.

A known wind turbine assembly comprises a heating resistor system for removing excessive moisture from electrical components of the wind turbine assembly. The heating resistor system comprises heating resistors for heating electric converters of the wind turbine assembly, the heating resistors being located outside the electric converters.

One of the disadvantages associated with the above known wind turbine assembly is that the heating resistor system requires space in the assembly, and incurs extra costs.

An object of the present invention is to provide a wind turbine assembly so as to alleviate the above disadvantages. The objects of the invention are achieved by a wind turbine assembly, which is characterized by what is stated in the independent claim. The preferred embodiments of the invention are disclosed in the dependent claims.

The invention is based on the idea of drying a grid side converter of a wind turbine assembly by short circuiting the grid side converter with controllable switches thereof, and supplying power from a generator of the wind turbine assembly through a generator side converter of the wind turbine assembly to the short circuited grid side converter for drying the grid side converter, wherein during the drying operation, voltage of the generator is kept so low that no breakthroughs occur, and currents in electrical components of the wind turbine assembly remain sufficiently low.

In an embodiment of the invention, a generator side converter is short-circuited first, and after the generator side converter is sufficiently dry, a grid side converter is short-circuited, and power is supplied to the short-circuited grid side converter by the previously dried generator side converter.

An advantage of a wind turbine assembly of the invention is its compact size and low costs due to possibility to omit a heating resistor system from the wind turbine assembly.

<FIG> shows a wind turbine assembly comprising a rotor system <NUM>, a generator <NUM>, a first converter <NUM>, a DC link <NUM>, a second converter <NUM>, an LC filter <NUM>, a brake chopper <NUM>, a circuit breaker <NUM>, a transformer <NUM>, an alternating current output <NUM>, a sensor system, and a controller system <NUM>.

The rotor system <NUM> is adapted to convert kinetic energy of wind into rotational energy of the rotor system <NUM>. The rotor system <NUM> comprises a plurality of adjustable blades <NUM>.

The generator <NUM> is adapted to be rotated by the rotor system <NUM> for converting the rotational energy of the rotor system <NUM> into electrical energy. The generator <NUM> is a permanent magnet generator, and is adapted to generate an alternating current. A voltage of the generator <NUM> is adapted to be controlled by adjusting blade angles of the plurality of adjustable blades <NUM>. In an alternative embodiment, the generator is a separately excited synchronous generator, and the voltage of the generator is adapted to be controlled by adjusting exciting current of the generator.

The first converter <NUM> has an alternating current side connected electrically to the generator <NUM>, and a direct current side connected electrically to the DC link <NUM> that comprises DC link capacitance. The second converter <NUM> has a direct current side connected electrically to the direct current side of the first converter <NUM> through the DC link <NUM>, and an alternating current side connected electrically to the alternating current output <NUM> of the wind turbine assembly through the LC filter <NUM>, the transformer <NUM> and the circuit breaker <NUM>.

Herein, two components are defined to be connected electrically to each other when there is a connection between the components enabling transfer of electric energy between the components.

Referring now to <FIG>, the alternating current side of the first converter <NUM> is connected electrically to phases U1, V1 and W1, and the alternating current side of the second converter <NUM> is connected electrically to phases U2, V2 and W2. The DC link <NUM> comprises a positive busbar DC+ and a negative busbar DC-, to which the direct current sides of the first converter <NUM> and second converter <NUM> are connected electrically.

The first converter <NUM> comprises a first bridge circuit having six switch members, and the second converter <NUM> comprises a second bridge circuit having six switch members. Each of the switch members has a controllable switch and a diode connected antiparallel with the controllable switch. The controllable switches of the first bridge circuit are denoted with reference signs S11 to S16, and corresponding diodes are denoted with reference signs D11 to D16. The controllable switches of the second bridge circuit are denoted with reference signs S21 to S26, and corresponding diodes are denoted with reference signs D21 to D26.

The controllable switches S11 to S16 of the first bridge circuit and the controllable switches S21 to S26 of the second bridge circuit are insulated-gate bipolar transistors, or IGBTs. In alternative embodiments, the controllable switches comprise other types of semiconductor switches such as field-effect transistors, or FETs.

The first converter <NUM> and second converter <NUM> are bidirectional converters. The first converter <NUM> and second converter <NUM> are functionally identical electric power converters.

The brake chopper <NUM> is connected electrically between the positive busbar DC+ of the DC link <NUM> and the negative busbar DC- of the DC link <NUM>. The brake chopper <NUM> comprises a brake chopper switch member and a brake resistor R10 connected in series. The brake chopper switch member comprises a controllable brake chopper switch S10 and a diode D10 connected antiparallel with the controllable brake chopper switch S10.

The LC filter <NUM> is connected electrically between the alternating current side of the second converter <NUM> and the transformer <NUM>. The LC filter <NUM> comprises an inductor and a capacitor. LC filters are known in the art. Herein, expression "LC filter" covers also LCL filters.

The controller system <NUM> is adapted to control the first converter <NUM> and second converter <NUM>, the brake chopper switch S10, and blade angles of the plurality of adjustable blades <NUM>. The controller system <NUM> is adapted to provide a drying operation for first converter <NUM>, a drying operation for the brake chopper <NUM>, a drying operation for second converter <NUM>, and a drying operation for additional electric system.

The drying operation for first converter comprises short circuiting the first converter <NUM> with the controllable switches of the first bridge circuit, and supplying power from the generator <NUM> to the short circuited first converter <NUM> for drying the first converter <NUM>. In the drying operation for first converter, the first converter <NUM> is short circuited by short circuiting the phases U1, V1 and W1 with the controllable switches of the first bridge circuit. During the drying operation for first converter, voltage of the generator <NUM> is kept lower than the nominal output voltage of the generator <NUM> by adjusting blade angles of the plurality of adjustable blades <NUM> with the controller system <NUM>.

In an embodiment, the drying operation for first converter comprises short circuiting the first converter <NUM> by controlling the controllable switches S11, S12 and S13 of the first bridge circuit to conducting state. In another embodiment, the drying operation for first converter comprises short circuiting the first converter <NUM> by controlling the controllable switches S14, S15 and S16 of the first bridge circuit to conducting state. In yet another embodiment, the drying operation for first converter comprises short circuiting the first converter <NUM> by controlling all of the controllable switches S11 to S16 of the first bridge circuit to conducting state.

The drying operation for the brake chopper is carried out subsequent to the drying operation for first converter. In an embodiment, the drying operation for the brake chopper is carried out subsequent to the drying operation for second converter. In an alternative embodiment, the drying operation for the brake chopper is carried out concurrently with the drying operation for second converter.

The drying operation for the brake chopper comprises controlling the brake chopper switch S10 to conducting state, and supplying power from the generator <NUM> through the first converter <NUM> to the brake resistor R10. In an embodiment, the drying operation for the brake chopper comprises controlling all of the controllable switches S11 to S16 of the first bridge circuit to non-conducting state, wherein power is supplied through the first converter <NUM> via diodes D11 - D16.

The drying operation for second converter is carried out subsequent to the drying operation for first converter. The drying operation for second converter comprises short circuiting the second converter <NUM> with the controllable switches of the second bridge circuit, and supplying power from the generator <NUM> through the first converter <NUM> to the short circuited second converter <NUM> for drying the second converter <NUM>.

The drying operation for second converter comprises short circuiting the second converter <NUM> by providing a short circuit between the positive busbar DC+ and negative busbar DC- with the controllable switches of the second converter <NUM>. In an embodiment, the drying operation for second converter comprises short circuiting the second converter <NUM> by controlling all of the controllable switches S21 to S26 of the second bridge circuit to conducting state. In another embodiment, the drying operation for second converter comprises short circuiting the second converter <NUM> by controlling the controllable switches S21 and S24 of the second bridge circuit to conducting state. In yet another embodiment, the drying operation for second converter comprises short circuiting the second converter <NUM> by controlling the controllable switches S22 and S25 of the second bridge circuit to conducting state. In yet another embodiment, the drying operation for second converter comprises short circuiting the second converter <NUM> by controlling the controllable switches S23 and S26 of the second bridge circuit to conducting state.

During the drying operation for second converter, power is supplied through the first converter <NUM> for example by controlling the controllable switches of the first bridge circuit to non-conducting state by the controller system <NUM>, wherein power is supplied from the first converter <NUM> to the short circuited second converter <NUM> through the diodes D11 - D16 of the first bridge circuit.

During the drying operation for second converter, voltage of the generator <NUM> is kept lower than the nominal output voltage of the generator <NUM> by adjusting blade angles of the plurality of adjustable blades <NUM> with the controller system <NUM>. Further, during the drying operation for second converter, the controller system <NUM> is adapted to control voltage of the generator <NUM> such that currents of the generator <NUM>, first converter <NUM> and second converter <NUM> are lower than or equal to corresponding nominal currents.

Since DC link <NUM> is located between the first converter <NUM> and second converter <NUM>, the drying operation for second converter inherently also dries the DC link <NUM>. In an embodiment, duration of the drying operation for second converter is determined based on humidity information from both the second converter and the DC link.

The alternating current output <NUM> of the wind turbine assembly is adapted to be connected to an electrical network. The circuit breaker <NUM> is located electrically between the transformer <NUM> and the alternating current output <NUM> of the wind turbine assembly. Therefore, the circuit breaker <NUM> is adapted to disconnect the alternating current side of the second converter <NUM> from the alternating current output <NUM> of the wind turbine assembly.

During the drying operation for first converter, the drying operation for the brake chopper, the drying operation for second converter and the drying operation for additional electric system, the circuit breaker <NUM> is in non-conducting state. Consequently, the drying operation for first converter, the drying operation for the brake chopper, the drying operation for second converter, and the drying operation for additional electric system are carried out by energy supplied by the generator <NUM>.

The sensor system comprises a humidity sensor <NUM> for measuring humidity relating to the first converter <NUM>, a temperature sensor <NUM> for measuring temperature relating to the first converter <NUM>, a humidity sensor <NUM> for measuring humidity relating to the second converter <NUM>, and a temperature sensor <NUM> for measuring temperature relating to the second converter <NUM>.

The sensor system is communicatively connected to the controller system <NUM>. The controller system <NUM> is adapted to terminate the drying operation for first converter when information received from the sensor system indicates that a humidity level of the first converter <NUM> has dropped to an acceptable level. Further, the controller system <NUM> is adapted to terminate the drying operation for second converter when information received from the sensor system indicates that a humidity level of the second converter <NUM> has dropped to an acceptable level. When humidity levels of the first converter <NUM> and second converter <NUM> are on acceptable levels, the first converter <NUM> and second converter <NUM> can be operated normally.

In an alternative embodiment, the controller system <NUM> is adapted to terminate the drying operation for second converter when a humidity level of the second converter has dropped to an acceptable level, and to terminate the drying operation for additional electric system when a humidity level of the additional electric system has dropped to an acceptable level. In another alternative embodiment, each drying operation has a predetermined duration, wherein the humidity levels are assumed to be on acceptable levels after the predetermined durations.

The drying operation for additional electric system is carried out subsequent to the drying operation for second converter. The drying operation for additional electric system comprises providing a drying current in at least one additional electric system for drying the at least one additional electric system, the drying current being lower than or equal to corresponding nominal current. Power for the drying current in the at least one additional electric system is supplied from the generator through the first converter and second converter.

The drying operation for additional electric system comprises controlling all of the controllable switches S11 to S16 of the first bridge circuit to non-conducting state, wherein power is supplied through the first converter <NUM> via diodes D11 - D16, and controlling the controllable switches S21 to S26 of the second bridge circuit such that suitable heating current flows through the capacitor of the LC filter <NUM>.

In an alternative embodiment, the drying operation for additional electric system comprises controlling all of the controllable switches S11 to S16 of the first bridge circuit to non-conducting state, and controlling switches S22 and S24 of the second bridge circuit to conducting state, wherein power is supplied through the first converter <NUM> and switches S22 and S24 to the transformer, and heat is generated in the transformer <NUM> for drying the transformer <NUM>.

Claim 1:
A wind turbine assembly comprising:
a rotor system (<NUM>);
a generator (<NUM>) for generating an alternating current, the generator (<NUM>) having a nominal output voltage, and being adapted to be rotated by the rotor system (<NUM>);
a first converter (<NUM>) having an alternating current side connected electrically to the generator (<NUM>), and a direct current side, the first converter (<NUM>) comprising a first bridge circuit having a plurality of switch members each having a controllable switch and a diode connected antiparallel with the controllable switch;
a second converter (<NUM>) having a direct current side connected electrically to the direct current side of the first converter (<NUM>), and an alternating current side, the second converter (<NUM>) comprising a second bridge circuit having a plurality of switch members each having a controllable switch; and
a controller system (<NUM>) adapted to control the first converter (<NUM>) and second converter (<NUM>),
characterized in that the controller system (<NUM>) is adapted to provide a drying operation for second converter comprising:
short circuiting the second converter (<NUM>) with the controllable switches of the second bridge circuit; and
supplying power from the generator (<NUM>) through the first converter (<NUM>) to the short circuited second converter (<NUM>) for drying the second converter (<NUM>),
wherein during the drying operation for second converter, voltage of the generator (<NUM>) is lower than the nominal output voltage of the generator (<NUM>) and
wherein the voltage of the generator is kept so low that no breakthroughs occur, and currents in electrical components of the wind turbine assembly remain sufficiently low.