KR100943696B1 - Method of controlling a wind turbine connected to an electric utility grid - Google Patents

Abstract

The present invention relates to a method of controlling a wind turbine connected to an electric utility grid during a malfunction in the electric utility grid 9. The method includes detecting a malfunction in the electrical utility grid and operating at least two control units of the power converter 12 with respect to at least one power conversion limit value. The present invention relates to a control system and a wind turbine for a wind turbine connected to a utility grid.

Description

How to control a wind turbine connected to an electric utility grid}

The present invention relates to a method of controlling a wind turbine connected to said electric utility grid in the event of a malfunction of the electric utility grid, a control system according to the preamble of claim 10 and a wind turbine according to the preamble of claim 15.

Typically, the wind turbine is connected to an electrical utility grid to generate power and supply it to consumers away from the wind turbine. The power is sent to the consumer via utility grid transmission or distribution lines.

Wind turbines and other utility grids connected to the power generating means are generally protected from malfunctions of the utility grid by grid disconnection switches. The disconnector disconnects the wind turbine from the utility grid upon detection of a malfunction. The malfunction can be defined, for example, as a grid shift over some specific limit of voltage drop +/- 5% or more with respect to the nominal value of the grid voltage.

Malfunctions in the utility grid can include, to some extent, several significant voltage drops within a short period of time, such as sags or "brownouts," which are among the most common known power disturbances in the utility grid. have.

The problem with grid disconnection of wind turbines is the fact that the magnitude or duration of voltage changes can be increased by the loss of power generation from the wind turbine generator. In addition, disconnected wind turbines require some time before the wind turbine is reconnected to the utility grid. The disconnection of the wind turbine affects the generation of power from the wind turbine and thus the profitability.

Other solutions have been proposed in the prior art for instantaneous compensation of wind turbines for one short grid malfunction. However, modern variable speed wind turbines can be damaged if the voltage on the utility grid suddenly disappears and disconnects from the grid. Damage may be caused by the surge voltage at the rotor side of the wind turbine generator or at the frequency converter. In addition, wind turbines can be damaged when the grid voltage returns due to the large current flow, especially the large current flow into the frequency converter.

The prior art disclosed in DE-A 102 06 828 proposes the use of resistors and power transistors in the DC link between the rectifier and inverter circuits and connected in parallel with the capacitors of the DC link. The resistor can be opened and closed to discharge the capacitor and thus eliminate short voltage spikes.

One of the objects of the present invention is to establish a technique for controlling wind turbines without the above mentioned disadvantages during severe malfunctions of the electric utility grid.

It is an object of the present invention to create a technique which is particularly flexible and thus protects wind turbines during utility grid malfunctions as well as immediately upon removal of the malfunctions regardless of the fault condition.

The present invention relates to a method of controlling a wind turbine connected to said electric utility during a malfunction of an electric utility grid, said method operating at least two control units of said power converter in relation to at least one power converter limit value. It comprises the step of.

This establishes a method that does not include the above mentioned disadvantages. It is an advantage that the method allows more flexible control of the protection means during grid failure, where a very large number of different approaches can be chosen to deal with grid failures and their exact consequences.

In particular, it is possible to reduce the dV / dt value and thus avoid voltage or current sparks, which can damage the conversion of the power converter, for example.

In one aspect of the invention, the at least two control units are operated in relation to the minimum and maximum limit voltage values of the DC link in the power converter to maintain the voltage value of the DC link between the minimum and maximum limit voltage values. This makes it possible to add or subtract the control unit in relation to the voltage, temperature value or further working value representing the transducer in order to satisfy and suppress the result of the malfunction.

In one aspect of the invention, the control unit comprises a grid side circuit of an electrical generator and a power converter operable to disconnect the power converter from the electrical generator and the electrical utility grid upon reaching the minimum or maximum limit value of the DC link. Include. In this way, it is possible to protect the power converter even if the grid failure is so severe that it cannot be compensated instantaneously from the utility and grid without disconnection. In addition, it is possible to maintain some minimum value, such as the DC link voltage and converter frequency value, which will be the initial working value of the power converter upon return to the utility grid's normal function.

In one aspect of the invention, the control unit further comprises at least one register block connecting at least one register between the busbars of the DC link in the power converter. In this way, it is possible to transfer power from the capacitor of the DC link to the ground plane through the resistor and thus reduce the DC link voltage.

In one aspect of the invention, the at least one resistor is openable to be connected to the busbar. This makes it possible to reduce the burden facing the register block with respect to the continued operation of the register block.

In one aspect of the invention, each register block is opened and closed at a frequency that depends on the voltage value of the DC link. This makes it possible to optimize the power reduction with respect to the register block and the switch of the power converter.

In one aspect of the invention, the resistor block is continuously activated when the voltage value of the DC link rises. This makes it possible to adapt the block to the relevant value of the fault condition.

In one aspect of the invention, each register block is activated for a limited period of time. This makes it possible to render the block inoperable for a very long period of time which damages the control system.

In one aspect of the invention, each register block is operated and activated with respect to the block temperature. This makes it possible to control the block more precisely and thus to extend the active period of the block.

The invention also relates to a control system, the system further comprising at least two control units of the power converter controlled in relation to at least one power converter limit value during the malfunction. This establishes an advantageous control system.

In one aspect of the invention, the at least two units comprise a plurality of register blocks, each block comprising at least one register and a switch. This makes it possible to control the blocks individually and to optimize the power reduction.

In one aspect of the invention, the resistor block further comprises a temperature measuring means.

In one aspect of the invention, the at least two units also comprise a grid side circuit of the power converter which is connected to each other by the generator and the DC link of the power converter.

In one aspect of the invention, the system comprises means for measuring a DC link voltage value and means for comparing the value with a limit value, such as a minimum or maximum limit voltage value of the DC link at the power converter.

The invention also relates to a wind turbine comprising at least two units of said power converter controlled in relation to at least one power converter limit value.

In one aspect of the invention, the at least two units of the power converter are located away from each other, such as in other locations in the engine compartment. This makes it possible to minimize the size of the required cooling means of each unit as well as to remove heat influences from other units.

The invention will be explained below with reference to the drawings.

1 shows a large modern wind turbine.

2 shows an embodiment according to the invention of a wind turbine generator having a frequency converter connected to a utility grid.

3 shows a part of a frequency converter.

4A and 4B schematically show an example of an over-voltage control unit and a gate driver control signal for the unit.

5 shows a control system for an over-voltage control unit.

6 shows the curve of the utility grid voltage and the corresponding curve of the intermediate DC voltage upon utility grid failure.

7 shows the corresponding curve of the gate driver control signal and the intermediate DC voltage of the over-voltage unit.

8 shows the temperature curve of a wind turbine in the event of a utility grid failure.

1 shows a modern wind turbine 1 with a tower 2 and a wind turbine engine compartment 3 located at the top of the tower. The wind turbine rotor 5, comprising three wind turbine blades, is connected to the engine compartment via a low speed shaft extending to the front of the engine compartment.

As shown in the figure, winds above a certain level enable the wind turbine rotor and rotate in a direction perpendicular to the wind due to the blade-induced lift. The rotational movement is converted into power, which is fed to the utility grid.

2 shows a preferred embodiment of a variable speed wind turbine comprising a dual feed induction generator 6 and a frequency and power converter 12 connected to the rotor of the generator.

The electric generator 6 comprises a stator 7 which is connected to the utility grid via a three-phase transformer 8 and a disconnector 11, and directly connects to the utility grid P _St (active stator power) and Q _St ( Reactive stator power) or provide power from the utility grid.

The rotor of the generator is mechanically driven by wind turbine rotor 5 (shown in FIG. 1) via a low speed shaft, a transmission means and a high speed shaft (not shown). In addition, the rotor is electrically connected to the frequency converter 12. The frequency converter 12 may convert the variable AC voltage into an intermediate DC voltage and then into a fixed AC voltage having a fixed frequency.

The frequency converter 12 includes a rotor side converter circuit 13 to rectify the AC voltage of the generator 6 to the DC voltage of the DC link 14 or to convert the DC voltage into an AC voltage supplied to the rotor of the generator. do. The DC link smoothes the DC voltage through the DC link capacitor (C). The grid side converter circuit 15 converts the DC voltage to an AC voltage having the desired frequency or vice versa. The rotor 15 power, which is P _r (active rotor power) and Q _r (reactive rotor power), with the resulting AC voltage and the desired frequency, passes through the transformer 8 to the utility grid (or from the grid). Delivered.

The wind turbine can be controlled to supply power from the generator to the utility grid at a constant voltage and frequency, regardless of the wind and wind turbine rotor speed varying from the generator.

The DC link comprises at least two over-voltage control units (B1, Bn), a resistor block, connected between two bus bars of the DC link. Each control unit is connected in parallel with the DC link capacitor C and includes at least a resistor R and a controllable power switch SP in series connection. This embodiment of the control unit also includes an anti parallel diode for the resistor and the power switch. Wherein the power switch is to send a current through the resistor thereby to be turned on and off in order to consume the electric power (P _1, P _n) in the register. The DC link voltage U _DC can be lowered as charge is removed from the DC link capacitor by sending a current through the resistor of the control unit. As a result, the power generated by the electric generator can be consumed as power P ₁ , P _n in the over-voltage control unit during periods when it is not possible to send some or all of the power P _R to the utility grid. .

For example, the disconnector 11 of the stator and rotor causes the electric generator to be disconnected from the utility grid in connection with maintenance work on the wind turbine or isolation from the utility grid. In addition, wind turbines can be disconnected from the utility grid if grid failures associated with significant voltage drops persist for longer periods of time.

3 shows a portion of a frequency converter comprising a rotor side converter circuit and a branch of the DC link. The branch includes two power switches SP, such as an insulated gate bipolar transistor (IGBT) with a phase of a three-phase pulse width modulation (PWM) frequency converter and having an anti-parallel diode.

The DC link capacitor C and at least two over-voltage control units B ₁ , B _n are connected to the positive and negative busbars of the DC link.

In addition, the figure shows schematically how much power is consumed in the resistors of at least two over-voltage control units B ₁ , B _n and thus lowers the DC link voltage. The switch of the unit is controlled such that the power may be consumed in a resistor at the same time or in different periods in relation to the over-voltage value and / or temperature of the frequency converter comprising the unit, as will be described further below.

4A and 4B schematically show an over-voltage control unit having an example of gate driver control signals G1 and G2 for controlling the unit.

4A shows an embodiment of the invention with respect to four over-voltage control units B ₁ to B ₄ connected in parallel with the busbar system of the DC link 14 and in parallel with the DC link capacitor C. FIG.

Each control unit is schematically shown as comprising a switch SP controlled by a register R and a gate driver control signal G1 or G2. The first control signal G1 is used to control the first two control units B ₁ , B ₂ , ie the same amount of power is consumed inside a unit in a different location, for example an engine room or a tower of a wind turbine. . The second control signal G2 is used to control the last two control units B ₃ , B ₄ , ie the same amount of power is consumed in different location units.

4B shows an example of gate driver control signals G1 and G2 for controlling the unit. The figure shows a first signal G1 which changes a low off value to a high on value in a certain period, whereby the over-voltage control units B1 and B2 will consume power. Subsequently, the second signal G2 will change the low off value to a high on value in a certain period, whereby the over-voltage control units B ₃ and B ₄ will consume power.

The above example indicates that the over-voltage control unit is controlled to consume power at different durations of different durations, ie different amounts of power are consumed at the control unit.

However, many strategies can be selected for the individual control unit, such as for example, using a register of the same or different value, or controlling at different time times. The choice of register value and duration makes it possible for the control unit to divide the amount of power which, for example, faces the same or different amounts of power in each unit.

5 shows an embodiment of a control system for an over-voltage control unit according to the invention.

에 대한 많은 입력 값들을 포함한다. The system comprises a microprocessor from measuring means such as the measured voltage value of the electrical utility grid U _Net , the DC link voltage value U _DC of the frequency converter 12 and the temperature of the control units B ₁ -B _n .

Contains many input values for.

The microprocessor further includes a parameter and a connection to the data store PS, which store the limits and thresholds such as maximum and minimum DC link voltage values and temperature values.

The maximum value defines a dangerous and potentially damaging over-voltage for the switch of the frequency converter. The minimum value defines an under-voltage that generates a dangerous and potentially damaging current that flows through the switch of the frequency converter.

The temperature limit value defines a temperature value that can damage the control unit or the frequency converter itself. The limit value may also include a time value, such as the longest period in which the control unit is active and facing power. In addition, a threshold voltage or temperature value may be stored in the reservoir, defining a situation in which values should be initiated such as activating more control units.

Other values such as an over-current value representing a shorter termination of the control signal for the switch of the frequency converter, for example to limit the rotor current of the dual feed induction generator of the wind turbine, will be stored in the reservoir.

The microprocessor controls many control units B1-Bn through gate drivers GD ₁ -GD _n in relation to the values to be measured and stored. The figure shows that each gate driver controls two control units and usually has the same gate driver control signal for the switch of the control unit. However, it should be understood that each control unit can be individually controlled by a microprocessor and the gate driver or two or more units can be controlled by only one gate driver. Preferred embodiments of the control system may be associated with two or four control units, but other numbers may be chosen if there is an advantage in a given application, such as more units in very high power frequency converters.

6 shows an example of a curve for utility grid voltage U _Net and a corresponding curve for intermediate DC link voltage U _DC at utility grid failure.

In the above example, the utility grid voltage is schematically shown as a curve that rapidly decreases from a nominal value to a value very close to zero during the period of grid failure.

The corresponding curve for the DC link voltage includes a slope because of the energy storage of the DC link capacitor. However, the value also decreases and the rotor switch and grid side converter circuits are deactivated and thus eventually reach the value (U _DCmin ) separating the frequency converter from the electric generator and utility grid. In addition, the control unit connected between the busbars of the DC link is deactivated and consequently the discharge of the DC link capacitor is stopped. This removes the utility grid fault and the utility grid voltage to maintain the voltage (U _DC) until regain the nominal value of the value (U _DCmin), in which case the voltage (U _DC) is also returned to normal values.

The initial current value is thereby limited to the voltage U _DC held at the value U _DCmin until the grid voltage returns.

7 further shows the corresponding curves for the gate driver control signals G1, G2 and the intermediate DC voltage U _DC at grid failure for a number of over-voltage control units in the control system.

The figure initially shows how for the first time a grid failure causes an over-voltage increase to a value of U ₁ (value close to U _max ). In order to protect the frequency converter and the wind turbine both gate driver control signals are at high level values and thus activate the corresponding control unit. After a period of time the voltage drops to a value lower than U ₄ and one control signal becomes a low level value; Deactivate the corresponding control unit, and then the other control signal becomes a low level value; Deactivate the final control unit as the voltage continues to drop. By deactivating all control units the voltage rises again and the control system can reactivate one or more control units to control the voltage until the grid fault disappears.

8 shows the temperature curve of the control unit of the wind turbine during a utility grid failure in which the failure starts at time t1. The one or more control units are activated at this time and require power due to the limit of over-voltage in the DC link of the frequency converter. As a result, the temperature curve increases and at time t2 the temperature limit T _max is reached for the active control unit. The microprocessor further activates the control unit and the temperature drops to the temperature limit T _min at time t3 and as a result at least one unit is deactivated. The number of such controls of the active control unit continues until the grid failure disappears.

So far, the present invention has been illustrated with respect to the above specific examples.

However, it should be understood that the present invention is not limited to the specific examples mentioned above and can be used in a wide variety of applications, such as multiple wind turbines connected to the same frequency converter. In addition, the application may further be associated with induction or synchronous generators of wind turbines connected with common frequency converters.

In addition, it should be understood that the frequency converter in particular will be designed in a wide variety of thyristor-based rectifier and inverter systems.

In addition, it should be understood that the present invention will utilize a wide variety of measured values if, for example, various measured values such as current values instead of voltage values correspond directly or indirectly to the above mentioned voltage and temperature values. The position of the measurement in the wind turbine system can also be changed if the measurement corresponds to at least the one developed above at least over the grid failure time.

1.wind turbine

2. Wind Turbine Tower

3. Wind turbine engine room

4, wind turbine hub

5. wind turbine rotor

6. Induction generator

7. Stator side of the generator including connection with disconnect switch and grid transformer

8. Utility grid transformer

9. Utility grid or network with voltage U _Net

10. Rotor side of generator including connection with frequency converter

12. Frequency converter

13. Rotor side converter circuit

14. DC link between rotary vane and grid side converter circuit

15. Grid side converter circuit

16. Disconnect switch and grid transformer and converter connection

17. Control system for over-voltage control unit

Overvoltage control unit of B _n number n

C DC Link Capacitor

D-power switch and reverse-parallel diode

En enable control signal

Gate control signal of Gn number n

Gate driver with GDn number n

I current

P _R , Q _R Active and Reactive Rotor Power Flow

P _St , Q _St Active and Reactive Stator Power Flow

Power flow through the control unit during P ₁ , P _n over-voltage situations

PS parameter / data storage

R register

Power switches, such as SP insulated gate bipolar transistors (IGBTs)

t time [sec]

T temperature [Celsius]

U voltage [volts]

U _Net Utility Grid Voltage

Voltage at U _DC DC link

Claims (17)

A method for controlling a wind turbine, wherein the wind turbine comprises an electrical generator and a power converter connected to the electrical utility grid in the event of a malfunction of the electrical utility grid. Detecting a malfunction in the electrical utility grid, and Operating at least two control units of the power converter in relation to at least one power converter limit value and at least one value relating to the control units or power converter, And wherein said actuating is performed in relation to temperature and active time periods of said control units or power converter as at least one value relating to said control units or power converter. The minimum or maximum threshold voltage value of the DC link in the power converter, in order to maintain the voltage value of the DC link in the power converter between a minimum and maximum threshold voltage value. A control method of a wind turbine, characterized in that it is operated in relation to. 3. The power supply of claim 1 or 2, wherein the control units are operative to disconnect the power converter from the electrical generator and the electrical utility grid when the control unit reaches the minimum or maximum limit value of the DC link. A control method for a wind turbine comprising grid side circuits of a power converter. 3. The method of claim 1, wherein the control units further comprise one or more register blocks connecting at least one resistor between busbars of a DC link in the power converter. 4. . The method of claim 4, wherein the at least one resistor is switchable to be connected to the busbars. 6. A method according to claim 4 or 5, wherein each register block is switched at a frequency dependent on the voltage value of the DC link. The method of claim 4, wherein the register blocks are continuously activated as the voltage value of the DC link increases. 5. A method according to claim 4, wherein each register block is active in limited time periods. 5. A method according to claim 4, wherein each register block is operated and activated in relation to its block temperature. The method of claim 1, wherein at least the temperature is measured directly or indirectly. A control system for controlling a wind turbine connected to the electrical utility grid in the event of a malfunction of the electrical utility grid, wherein the control system Means for detecting a malfunction of the electrical utility grid; And Includes power inverter, The system includes at least two control units (B ₁ -B _n ) of the power converter controlled in relation to the at least one power converter limit value and at least one value relating to control units or power converters in the event of a malfunction. More, Said control being performed in relation to temperature and active time periods of said control units or power converter as at least one value relating to said control units or power converters. 12. The control system according to claim 11, wherein said at least two units comprise a plurality of register blocks and each block comprises at least one register (R) and a switch (SP). 13. The control system of claim 12, wherein the register blocks further comprise temperature measuring means. 12. The control system of claim 11, wherein the at least two units also comprise grid side circuits of a power converter connected to each other by a DC link of a generator and a power converter. 15. The apparatus of claim 14, wherein the control system comprises means for measuring the DC link voltage value and means for comparing the value at the power converter with a limit value, such as a minimum or maximum limit voltage value of the DC link. Control system characterized in that. 12. The control system of claim 11, wherein the means measures at least the temperature directly or indirectly. In a wind turbine connected to the utility grid 9, The wind turbine, Electric generator (6) A power converter 12 connected with the electric generator and utility grid, and 15. A control system according to any one of claims 11 to 14, comprising at least two control units of said power converter controlled in relation to at least one power converter limit value, The control is characterized in that the wind turbine is further performed in relation to temperature and active time periods of the control units or power converter.

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