Patent ID: 12196178

DETAILED DESCRIPTION

The illustration in the drawing is schematic. It is noted that in different figures, similar or identical elements are provided with the same reference numerals or with reference numerals which differ only within the first digit.

FIG.1shows a wind farm100comprising a mix of ordinary wind turbines114and black start enabled wind turbines110. The wind turbines110,114are arranged in rows and interconnected by cables122connected to a common feeder120which is connected to utility grid160via main breaker switch140and transformer150. The common feeder120and cables122form a wind farm grid. Each black start enabled wind turbine110is connected to its own dedicated power generator/storage unit112which is configured to supply auxiliary power to the black start enabled wind turbine110when the wind farm grid120,122is deenergized. The wind farm100further comprises a wind farm controller130configured to receive internal input132from one sensor device142on the wind farm side of the main breaker switch140and from another sensor device144on the grid side of the main breaker switch140. Measurements on both sides of the wind farm breaker is an optional feature but enables the wind farm controller130to resynchronize and connect the wind farm to the utility grid160when this part of the network has been energized. The internal input132to controller130may include measurement values of voltage frequency and magnitude on both the wind farm side and the utility grid side of main breaker switch140. Furthermore, the internal input132may include a status of the main breaker switch140. The controller130is further configured to receive external input134, e.g., from a utility grid operator (not shown). The controller130is connected to a wind farm communication network136which (at least during normal operation) allows the controller130to communicate with each individual wind turbine110,114in the wind farm100.

The black start enabled wind turbines110are capable of operating in a black start mode to produce and provide electrical power in order to energize the wind farm grid120,122in case of a power outage where no power is available from the utility grid160.

FIG.2shows a flowchart of a method200of performing a black start in a wind farm100(seeFIG.1) in accordance with an embodiment. Here, one of the black start enabled wind turbines110is preselected as a primary black start enabled wind turbine T1and the remaining black start enabled wind turbines110are preselected as secondary black start enabled wind turbines T2, T3.

In embodiments, the method200begins at210by starting the primary black start enabled wind turbine T1in black start mode in order to supply voltage to the wind farm grid and thereby cause the voltage in the wind farm grid to increase. This may occur in response to receiving a black start initiation signal at the primary black start enabled wind turbine T1, either through an operational part of the communication network136or through a dedicated communication channel (not shown).

At220, the at least one secondary black start enabled wind turbine (FIG.1shows two secondary black start enabled wind turbines T2, T3) monitors an electric parameter value in the wind farm grid, such as a voltage magnitude, a frequency, or a code modulated onto the voltage. At this time, each of the secondary black start enabled wind turbines T2, T3may be operated in a black start stand-by mode, where the rotors are spinning and the converters are energized, etc.

The secondary black start enabled wind turbines T2, T3may start operating in the black start stand-by mode in response to receiving the above-mentioned black start initiation signal.

At230, the at least one secondary black start enabled wind turbine T2, T3is started in black start mode in order to supply voltage to the wind farm grid when the monitored electric parameter value meets a predetermined condition which may be individual for each secondary black start enabled wind turbine T2, T3. The predetermined condition may for example be met when the voltage level in the wind farm grid120,122is above a predetermined voltage threshold value, or when the voltage frequency in the wind farm grid is above or below a predetermined frequency threshold value, or when a code modulated onto the grid voltage is determined to correspond to a predetermined code. The predetermined condition may be different or identical for each of the secondary black start enabled wind turbines T2, T3. Alternatively, the predetermined condition may be a first predetermined condition for a first group of secondary black start enabled wind turbines110while the predetermined condition is a second predetermined condition for a second group of secondary black start enabled wind turbines110.

In short, the above procedure results in that the primary black start enabled wind turbine T1starts supplying power to the wind farm grid120,122, and that the secondary black start enabled wind turbines T2, T3joins it once their respective conditions are fulfilled, i.e., sequential one after the other, all together at essentially the same time, or in groups. The trigger for the secondary black start enabled wind turbines T2, T3to start operating in black start mode is individual conditions relating to an electric parameter value in the wind farm grid. Hence, no active interaction from the farm controller130or from any other control unit is needed in order to make the secondary black start enabled wind turbines T2, T3join the primary black start enabled wind turbine T1to perform a black start of the wind farm100. Once the primary black start enabled wind turbine T1has been started in black start mode, the other (secondary) black start enabled wind turbines T2, T3will join it as soon as their monitoring reveals that the corresponding conditions are met.

FIG.3shows a timing chart of control signals for operating black start enabled wind turbines in a wind farm during a black start in accordance with an embodiment. More specifically,FIG.3shows a plot310showing the wind farm grid voltage V as a function of time, a control signal321for a primary black start enabled wind turbine T1, a control signal322for a first secondary black start enabled wind turbine T2, and a control signal323for a third secondary black start enabled wind turbine T3. In this embodiment, the wind farm grid voltage V is monitored and used to determine when to start operating the secondary black start enabled wind turbines T2, T3in black start mode. The primary black start enabled wind turbine T1begins operating in black start mode at time t=t1when the corresponding control signal321shifts to ON. This causes the wind farm grid voltage V to increase along a first ramp segment311. When the wind farm grid voltage V reaches a first threshold value Vthres1at time t=t2, the first secondary black start enabled wind turbine T2determines that its predetermined condition is met and consequently switches to black start mode by toggling its corresponding control signal322to ON. The wind farm voltage continues to increase along a second ramp segment312. When the wind farm grid voltage V reaches a second threshold value Vthres2at time t=t3, the second secondary black start enabled wind turbine T3determines that its predetermined condition is met and consequently switches to black start mode by toggling its corresponding control signal323to ON. The wind farm voltage V then continues to increase along a third ramp segment313. At time t=t4, the wind farm grid voltage V reaches a level Vminwhich is the lowest voltage at which the complete wind farm may be safely operated without the risk of causing damage to the wind ordinary wind turbines. At time t=t5, the wind farm grid voltage V reaches a target level Vtargetwhich is the desired voltage level in the wind farm grid during normal operation. This level is maintained along segment314and the wind farm100can now be (re)connected to the utility grid160and, if necessary, contribute to restoring the utility grid voltage. Alternatively, the wind farm is operated in island mode as means to supply the islanded electrical load, which could be wind turbine and substation auxiliary load, and which could also include dedicated customers as e.g., an electrolyzes plant.

The energization, that is the complete voltage ramp from 0% to Vmin, must be completed fast enough to avoid damaging the electrical components, i.e., it is required that t4−t1≤TLimit. It is desirable to keep the time outside this window short, e.g., below 30 to 60 seconds, to avoid the risk of extended operation at voltage levels that the electrical components have not been verified for, or potentially much shorter, e.g., below 5 seconds, if electrical protection equipment cannot safely detect electrical faults during the voltage ramping. This is possible with embodiments of the present invention where the secondary black start enabled wind turbines T2, T3join the primary black start enabled wind turbine automatically in dependency of one or more conditions relating to a monitored electrical parameter value in the wind turbine grid120,122.

Although the present invention has been disclosed in the form of embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.