Back-up energy storage with in-rush current limiting for wind turbine pitch drive

Abstract

A wind turbine pitch drive system comprises an electric grid for supplying electrical power, a motor for driving a pitch actuator, an electronic converter for controlling the motor and a back-up energy storage unit for supplying electrical power. The electronic converter comprises a DC-link capacitor bank. The system furthermore comprises a switching device for selectively connecting the DC-capacitor bank link to the back-up energy storage unit, and a frequency generator for controlling the switching device. Also disclosed is a method for protecting a component of the electronic converter.

Claims

1. A wind turbine pitch drive system comprising: an electric grid configured to supply electrical power; a motor configured to drive a pitch actuator; an electronic converter configured to control the motor, the electronic converter including a DC-link capacitor bank; a back-up energy storage unit configured to supply electrical power; a switching device configured to selectively connect the DC-link capacitor bank to the back-up energy storage unit; and means for protecting the electronic converter from damaging in-rushing current by controlling the in-rushing current from the back-up energy storage unit to the DC-link, wherein the in-rushing current is the current that occurs when the back-up energy storage unit is substantially charged and the DC-link to which the back-up energy storage unit is connected is substantially discharged, and energy supply is switched to the back-up energy storage unit; and wherein the means for protecting comprises a frequency generator configured to generate a high frequency pulse based on a detected difference in voltage level between the back-up energy storage unit and the D-C link.

2. The system according to claim 1, wherein the back-up energy storage unit comprises at least one ultra-capacitor.

3. The system according to claim 1, wherein the back-up energy storage unit comprises at least one battery.

4. The system according to claim 1, wherein the switching device is an insulated gate bipolar transistor.

5. The system according to claim 1, wherein the switching device uses the high frequency pulse generated by the frequency generator to apply pulse width modulation to control the in-rushing current.

6. The system according to claim 1, wherein the switching device uses the high frequency pulse generated by the frequency generator to apply pulse frequency modulation to control the in-rushing current.

7. A method for protecting a component of an electronic converter in a wind turbine pitch drive system that includes: an electric grid configured to supply electrical power; a motor configured to drive a pitch actuator; an electronic converter configured to control the motor, the electronic converter including a DC-link capacitor bank; a back-up energy storage unit configured to supply electrical power; a switching device configured to selectively connect the DC-link capacitor bank to the back-up energy storage unit; and a frequency generator configured to control the switching device, the method comprising: detecting a difference between a voltage level of the DC-link capacitor bank of the electronic converter and a voltage level of the back-up energy storage unit such that the voltage level of the back-up energy storage unit is higher than the voltage level of the DC-link capacitor bank; generating a high frequency pulse, from the frequency generator, based on the detected difference in voltage level; and using the high frequency pulse to intermittently switch the switching device on and off to control an in-rushing current from the back-up energy storage unit.

8. The method according to claim 7, wherein the using of the high frequency pulse to intermittently switch the switching device comprises applying pulse modulation.

9. The method according to claim 8, wherein the pulse modulation applied is pulse width modulation.

10. The method according to claim 8, wherein the pulse modulation applied is pulse frequency modulation.

11. The method according to claim 7, wherein the detecting of a difference between the voltage level of the DC-link capacitor bank of the electronic converter and the voltage level of the back-up energy storage unit comprises measuring the voltage level of the back-up energy storage unit.

12. The method according to claim 7, wherein the detecting of a difference between the voltage level of the DC-link capacitor bank of the electronic converter and the voltage level of the back-up energy storage unit comprises measuring a voltage level at the DC-link capacitor bank.

13. The method according to claim 7, wherein the detecting of a difference between the voltage level of the DC-link capacitor bank of the electronic converter and the voltage level of the back-up energy storage unit comprises measuring a voltage level at the electric grid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Particular embodiments of the present invention will be described in the following by way of non-limiting examples, with reference to the appended drawing, in which:

(2) FIG. 1 illustrates an example wherein a wind turbine pitch drive comprises a controlled switching module between the back-up energy storage unit and the DC-link of the electronic power converter.

(3) FIG. 2 illustrates at least one battery (102) of the back-up energy storage unit (100) according to another embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

(4) The system and method disclosed herein provide protection to wind turbine pitch drives from in-rush currents discharged from the back-up energy storage unit during maintenance operations.

(5) The embodiment illustrated in FIG. 1 shows a pitch drive electrical system of a wind turbine. The 3 phases lines (W1, V1, U1) of the pitch drive motor (10) are each respectively connected to the 3 phases lines (L1, L2, L3) of the electrical grid, across the pitch drive electronic power converter (150). This pitch drive electronic converter may comprise a thyristor bridge (40) to rectify AC to DC power, a DC link capacitor bank (30) to stabilise the power and a power stage (20) to invert DC to AC power and a brake chopper (80) to dissipate excess energy, e.g. energy generated by the pitch drive motor (10) when it operates as a generator.

(6) Other components (152) such as a grid power choke (50), a grid contactor (60) and grid fuses (70) and a braking resistor (90) may also be included and are also represented on FIG. 1.

(7) In addition, this embodiment comprises a back-up energy storage unit (100) with multiple ultracapacitors which are in-turn connected to the DC-link capacitors (30) across a switching module (170) which comprises a switching device (110) and a frequency generator (160) for controlled modification of the in-rush currents (Idis) from the back up energy storage unit (100) when connected to the pitch drive electronic converter (150) during e.g. maintenance.

(8) Other components (152) such as back-up circuit fuses (120), a back-up circuit contactor (130) and back-up circuit diodes (140) may also be included and are also illustrated in this figure.

(9) In one embodiment, the controlled switching device (110) and the back-up circuit diodes (140) may be physically located within the pitch drive's power electronic converter (150). In other embodiments, the controlled switching device (110) and the frequency generator (160) and the back-up circuit diodes may be external to the pitch drive electronic converter. In this case, they may still be controlled by the electronic converter (150).

(10) In the present disclosure, the term ultracapacitor is to be interpreted as also referring to supercapacitors and electric double layer capacitors. In another embodiment the energy storage unit may comprise a battery (102) as shown in FIG. 2.

(11) During maintenance, the effect of connecting the energy storage unit's (100) charged ultracapacitors to the DC-link (30) across the switching module (170) is that of damping or dimming the in-rush current waveform in a controlled manner by modulating the duty cycle of the switching device (110), using e.g. pulse width modulation (PWM) or pulse frequency modulation (PFM) so that it is not harmful to the electronic components in the pitch drive electronic converter.

(12) In one embodiment, the frequency generator (160) may be a pulse generator (160). In one example, the pulse generator may be an electronic chopper.

(13) In some embodiments, the controlled switching device (110) may be an Insulated Gate Bipolar Transistor (IGBT). An IGBT is a three-terminal power semiconductor device primarily used as an electronic switch and in newer devices is noted for combining high efficiency and fast switching. In other embodiments, the controlled switching device may e.g. be a thyristor.

(14) One embodiment of the method of this invention may comprise detecting a voltage level in the electric grid supplied voltage below a predetermined threshold, generating a high frequency pulse, and controlling the high frequency pulse to intermittently switch the switching device on and off to dampen the in-rushing current from the energy storage unit's ultracapacitor by continuously adapting to the difference between the voltage level in the electric grid and the voltage level at the energy storage unit.

(15) In an alternative embodiment, the voltage at the DC-link may be otherwise used to perform said controlled switching, so that in this case the switching may be adapted to the voltage difference between the DC-link and the energy storage unit.

(16) Although only a number of particular embodiments and examples of the invention have been disclosed herein, it will be understood by those skilled in the art that other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof are possible. Furthermore, the present invention covers all possible combinations of the particular embodiments described. Thus, the scope of the present invention should not be limited by particular embodiments, but should be determined only by a fair reading of the claims that follow.