KR20140078229A - Method for compensating reactive power of offshore wind power generator in low voltage ride through of the power grid - Google Patents

Abstract

The present invention relates to a method for compensating for reactive power of a sea wind power generator in a low voltage of a grid, capable of stably supplying, to the grid, power produced in the sea wind power generator by compensating for the reactive power of the sea wind power generator when there is a low voltage in the grid in order to meet a grid low voltage ride through (LVRT) standard among domestic/foreign grid connected reference items. According to an embodiment of the present invention, the method for compensating for reactive power of a sea wind power generator includes the steps of: receiving, by a main controller of a power converting device in a sea wind power generating system, a voltage and a current of a grid connected to the sea wind power generator which is monitored from an inverter of the power converting device; determining, by the main controller of the power converting device, whether the received voltage of the grid is less than a predetermined grid reference voltage; calculating, by the main controller of the wind power generator in the sea wind power generating system, a reactive power value by using the voltage and the current of the monitored grid which are supplied by the main controller of the main power converting device if it is determined in the determining step that the received voltage of the grid is less than the predetermined grid reference voltage; and comparing, by the main controller of the wind power generator, the calculated reactive power value with a predetermined reactive power reference value to supply, to the main controller of the power converting device, a reactive power compensation value generated to compensate for a difference between the calculated reactive power value and the reactive power reference value.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for compensating reactive power of an offshore wind turbine during a low voltage system,

The present invention relates to a method for compensating reactive power of an offshore wind turbine during a system low voltage, and more particularly, to a method for compensating for reactive power of an offshore wind turbine when a low voltage is generated in a system satisfying a system low voltage compensation (LVRT) The present invention relates to a method for compensating reactive power of an offshore wind turbine at a low voltage system in which a power generated from an offshore wind turbine generator can be stably supplied to a system.

Recently, the price of wind power has been decreasing due to the progress of technology and national support, and it is actively proceeding worldwide.

In addition, due to the increase in the capacity of offshore wind farms worldwide, the amount of energy connected to the grid has also increased so that the stability and sustainability of offshore wind turbine and offshore wind farm operation have become important to affect the grid. In other words, when a power grid breaks down, the offshore wind farms are being changed to a special form that cooperates with the grid for continuous operation and grid stabilization. In recognition of the importance of grid stability, And to establish grid linkage criteria for system influences and limitations.

The existing grid linkage standard is mainly aimed at preventing single power operation of power inverter in the event of a grid accident. Recently, as the size of offshore wind power grid has been increasing, grid linkage standards have been proposed in cooperation with the grid. In particular, in the case of wind turbines, the ability to perform low voltage ride through (LVRT) is required. In case of low voltage system such as voltage drop pattern required by LVRT, it is standardized to maintain the connection between wind power generator and power system to continue wind power generation.

Therefore, there is a need for a method that can compensate the reactive power of the offshore wind turbine to meet the system low voltage compensation (LVRT) when low voltage is generated in the system.

It is an object of the present invention to provide a system and method for compensating reactive power of an offshore wind power generator when a low voltage is generated in a system so as to satisfy a system low voltage compensation (LVRT) The present invention provides a method for compensating reactive power of an offshore wind power generator in a system under low voltage.

According to an aspect of the present invention, there is provided an offshore wind power generation system for providing power generated by an offshore wind power generator to a system through a High Voltage Alternating Current (HVAC) Receiving a voltage and a current in a grid associated with the offshore wind turbine monitored from an inverter of the power inverter by a power inverter main controller of the offshore wind turbine system; Determining by the power converter main controller whether the voltage of the received grid is less than a predetermined grid reference voltage; Wherein when the voltage of the received grid is less than a predetermined grid reference voltage as a result of the determination of the wind power generator main controller of the offshore wind power generation system, Calculating a reactive power value; And a controller for comparing the calculated reactive power value with a predetermined reactive power reference value by the main controller of the wind power generator to calculate a value for reactive power compensation generated to compensate for a difference between the calculated reactive power value and the reactive power reference value, And supplying the main wind power to the main controller. The method for compensating reactive power of an offshore wind power generator is provided.

The receiving step preferably receives the voltage and current of the grid linked to the offshore wind power generator in the grid.

Preferably, the receiving further receives a power factor of the system associated with the offshore wind power generator in the system.

The main controller of the power conversion apparatus preferably controls the power conversion apparatus that constitutes the output voltage and output current of the power conversion apparatus by a multi-level pulse width modulation scheme.

Further, the method of compensating reactive power of offshore wind turbine according to an embodiment of the present invention may further include, after the providing step, And compensating the reactive power by performing power conversion using a multi-level pulse width modulation scheme.

According to another embodiment of the present invention, there is provided an offshore wind power generation system for providing power generated by an offshore wind power generator to a system via an HVAC (High Voltage Alternating Current) And if it is determined that the voltage of the received system is less than a predetermined system reference voltage, if it is determined that the received system voltage is less than a predetermined system reference voltage, To the outside of the system; And calculating a reactive power value using the voltage and current of the system provided from the main controller of the power conversion apparatus, comparing the calculated reactive power value with a preset reactive power reference value, and comparing the calculated reactive power value and the reactive power reference value And a wind turbine main controller for providing a value for reactive power compensation generated to compensate for the difference to the power converter main controller.

The main controller of the power conversion apparatus preferably controls the power conversion apparatus that constitutes the output voltage and output current of the power conversion apparatus by a multi-level pulse width modulation scheme.

The main controller of the power conversion apparatus performs power conversion based on the value for the reactive power compensation using the multi-level pulse width modulation scheme to compensate for the reactive power.

According to the embodiment of the present invention, the reactive power of the offshore wind turbine is compensated when the low voltage is generated in the system so as to satisfy the system low voltage compensation (LVRT) criterion among domestic and external grid connection standard items, There is an effect that can supply.

According to the embodiment of the present invention, since the output voltage of the power conversion apparatus controlled by the main controller of the power conversion apparatus is composed of a large number of multilevel pulse width modulation methods, there is no need to add a separate filter, And the output current can be supplied.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram for explaining an offshore wind power generation system implementing a reactive power compensation method of an offshore wind power generator in a grid low voltage state according to an embodiment of the present invention;
FIG. 2 is a flowchart illustrating a method for compensating reactive power of an offshore wind turbine generator in a system under low voltage according to an embodiment of the present invention; and
FIG. 3 is a graph illustrating an embodiment of a system requirement that requires a low voltage ride through (LVRT) function when a system under voltage is generated.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a view for explaining an offshore wind power generation system implementing a reactive power compensation method of an offshore wind power generator in a grid low voltage state according to an embodiment of the present invention.

Referring to FIG. 1, an onshore wind power generation system 1 according to an embodiment of the present invention generates power by rotating a blade 15 by a wind power generator 10 by wind power. The power obtained by the wind power generation is converted into DC power through the converter 20 and outputted to the DC bus. The inverter 30 is a DC-AC inverter that converts the DC power received from the DC bus into AC power having the same frequency as the power system. At this time, since the multi-level false-width modulation method of the power conversion device 40 is employed, it is not necessary to add a separate filter, and a sinusoidal waveform in which the output voltage and the output current are stable to the system can be supplied.

The offshore wind power generation system 1 according to the present invention is provided with a power conversion apparatus main body 1 for controlling the power conversion apparatus 40 including the converter 20, the DC bus (not shown) and the DC-AC inverter 30, (50) for providing a reactive power compensation value for compensating reactive power when generating a low voltage in the system based on the voltage and current of the system provided from the power inverter main controller (50) And a wind power generator main controller 60.

More specifically, the power inverter master controller 50 receives the voltage and current of the grid associated with the wind turbine 10 producing the power, that is, the grid connection point 2, and the voltage of the received grid 20 Is compared with a preset grid reference voltage to determine if a voltage of the received grid is below a predetermined grid reference voltage, that is, whether a low voltage has occurred at the grid connection point (2). Here, the voltage and the current of the grid connection point 2 are monitored by the DC-AC inverter 30 of the above-described power inverter 40 and the voltage and current of the grid associated with the offshore wind turbine generator 10, And receives the voltage and current of the system in the power inverter main controller 50.

Further, the power inverter main controller 50 also controls the power supply system main controller 50 so that when the voltage of the received grid connection point 2 is lower than the grid reference voltage, that is, when the low voltage is generated at the grid connection point 2, Provides the voltage and current of the grid linkage point (2) received at the wind turbine main controller (60) to compensate. If the voltage of the received grid linkage point 2 exceeds the grid reference voltage, that is, when a high voltage is generated in the grid, the voltage and current of the received grid line is also supplied to the wind turbine main controller 60 in order to control the high voltage. .

In addition, the power inverter main controller 50 receives the power factor of the grid connection point 2 and provides it to the wind turbine main controller 60. The main controller 60 of the wind turbine generator determines whether the received power factor satisfies the power factor criterion, and can adjust the power factor based on the power factor criterion if the power factor criterion is not satisfied. If the power factor is low, the voltage of the grid line may fluctuate and the reactive power may become large. Therefore, the main controller 60 of the wind turbine generator 60 may include a power factor adjusting unit (not shown) Compensate.

In this case, the power factor reference is set to 0.95 and 0.925 (0.925 lagging <PF <0.95leading). However, since the power factor is different for each country, the value set according to the country to which the present invention is applied Can be different.

The main controller 60 of the wind turbine generator calculates the reactive power value by applying the following equation (1) to the voltage, current, and power factor of the system 2 received from the main controller 50 of the power conversion apparatus.

는 수신된 역률(코사인값임)을 사인(sin)값으로 변환한 값이다.Where V is the voltage of the received grid linkage point 2, I is the current of the received grid linkage point 2,

Is a value obtained by converting the received power factor (cosine value) into a sin value.

Further, the main controller 60 of the wind turbine generator compares the calculated reactive power value with a predetermined reactive power reference value, and calculates a reactive power compensation value to compensate for the difference between the two, that is, the difference between the calculated reactive power value and the reactive power reference value And provides the generated reactive power compensation value to the power inverter main controller 50. [

Accordingly, the main controller 50 of the power conversion apparatus controls the DC-AC inverter 30 configured in the multi-level pulse width modulation scheme based on the value for reactive power compensation provided from the main controller 60 of the wind turbine generator 60, And the output current can supply a stable sinusoidal waveform to the system network 3. [ That is, the power inverter main controller 50 controls the DC-AC inverter 40 so as to compensate for the reactive power supplied to the grid connection point 2 associated with the offshore wind power generator 10.

On the other hand, the power generated by the offshore wind power generator 10 is transmitted to the grid connection point 2 via the submarine cable L. Here, the submarine cable (L) is a cable using HVAC (High Voltage Alternating Current).

The power grid 3 receives the power produced by the offshore wind power generator 10 via the grid connection point 2 associated with the offshore wind power generator 10. The grid connection point 2 is provided in the substation system in terms of data acquisition, operation management, and efficiency, and may include a transformer, a disconnector, a circuit breaker, an ancillary equipment, a lightning arrester, and a switchboard, which are not shown.

As described above, the offshore wind power generation system 1 of the present invention includes a power inverter main controller 50 and a wind turbine main controller 50 to implement a reactive power compensation method for compensating a low voltage when a low voltage is generated at the grid connection point 2, It is possible to compensate for the reactive power of the offshore wind turbine when a low voltage is generated in a system that can be flexibly applied to different grid linkage standards including each country (60).

FIG. 3 shows a graph of an embodiment of a system regulation requiring a low voltage ride through (LVRT) function when a system undervoltage occurs.

As shown in FIG. 3, when the grid connection point 2 is normally operated, the grid voltage PU is maintained at '1', but when a problem occurs at the grid connection point 2 and a low voltage is generated, PU) is suddenly decreased rapidly. Therefore, it is desired to contribute not only effective power generated in the offshore wind power generation system 1 but also reactive power for recovery of power, recovery of frequency variation, and the like within a very short time when a low voltage at which the voltage of the system 2 drops instantaneously , Which can compensate for the reactive power of the wind turbine (10), which is applied flexibly to different grid interconnections in different countries.

Hereinafter, a method for compensating for reactive power of an offshore wind turbine generator in a grid low voltage system according to the present invention will be described with reference to FIG. 2 through the above-described offshore wind power generation system 1.

FIG. 2 is a flowchart illustrating a method of compensating reactive power of an offshore wind turbine generator in a system under low voltage according to an embodiment of the present invention. Referring to FIG.

The main controller 50 of the offshore wind power generation system 1 receives voltage and current of the grid connection point 2 associated with the wind power generator 10 (S11). More specifically, the voltage and current of the system are monitored by the DC-AC inverter 30 of the power converter 40 controlled by the power inverter main controller 50. The voltage and current of the system 20 monitored by the DC-AC inverter 30 is received by the power inverter main controller 50. [ The power inverter main controller 50 additionally receives the power factor of the grid connection point 2 monitored by the DC-AC inverter 30. [

The power inverter main controller 50 compares the voltage of the received grid connection point 2 with a preset grid reference voltage to determine whether the voltage of the monitored grid 2 is less than the grid reference voltage (S13).

If it is determined in step S13 that the voltage of the received grid link point 2 exceeds the grid reference voltage, that is, when a high voltage is generated in the grid, the wind turbine main controller 60 controls the reactive power of the wind turbine generator And provides the reactive power control value to the power inverter main controller 50 (S16).

If it is determined in step S13 that the voltage of the received grid link point 2 is lower than the grid reference voltage, that is, when a low voltage is generated in the grid, the main controller 60 of the wind turbine generator 60 receives The voltage, current, and power factor of the grid connection point 2 are applied to Equation (1) to calculate the reactive power value (S15).

The main controller 60 of the wind turbine generator generates a value for reactive power compensation so as to compensate the difference between the reactive power value and the reactive power reference value by comparing the calculated reactive power value with a predetermined reactive power reference value, To the power inverter main controller 50 (S17).

The main controller 50 controls the power converter 40 to compensate for the reactive power of the wind turbine according to the reactive power compensation value provided from the main controller 60 (S19). That is, the main controller 50 of the power conversion apparatus performs power conversion based on the value for reactive power compensation using a multi-level pulse width modulation scheme to compensate for the reactive power.

Thus, when a low voltage is generated due to the problem of the grid 3 while the power generated by the offshore wind power generator 10 is supplied to the grid connection point 2 via the HVAC cable L, The power generated from the offshore wind power generator 10 can be stably supplied to the grid 3 without removing the offshore wind power generator 10 from the system 2 even if a low voltage is generated in the grid 3 Can supply. Accordingly, in the grid connection of the offshore wind power generation plant, the grid connection can be stably maintained due to the stabilization of the reactive power when the low voltage is generated in the grid network (3).

The invention being thus described, it will be obvious that the same way may be varied in many ways. Such modifications are intended to be within the spirit and scope of the invention as defined by the appended claims.

1: offshore wind power generation system 2: grid connection point
3: grid network 10: offshore wind power generator
15: blade 20: converter
30: inverter 40: power converter
50: Power conversion device main controller 60: Wind power generator main controller
L: Submarine cable

Claims (8)

A method for compensating reactive power of an offshore wind power generator using a offshore wind power generation system that provides power generated by a offshore wind power generator to a system through a High Voltage Alternating Current (HVAC)
Receiving the voltage and current of the grid connected to the offshore wind turbine monitored from the inverter of the power inverter by the power inverter main controller of the offshore wind power system;
Determining by the power converter main controller whether the voltage of the received grid is less than a predetermined grid reference voltage;
Wherein when the voltage of the received grid is less than a predetermined grid reference voltage as a result of the determination of the wind power generator main controller of the offshore wind power generation system, Calculating a reactive power value; And
A reactive power compensation value generated to compensate for a difference between the calculated reactive power value and the reactive power reference value by comparing the calculated reactive power value with a predetermined reactive power reference value by the wind power generator main controller, Wherein the step of supplying the reactive power to the wind power generator includes the step of providing the power to the wind power generator. The method according to claim 1,
Wherein the receiving step receives the voltage and current of the grid associated with the offshore wind power generator in the system. The method of claim 2,
Wherein the receiving further receives a power factor of the grid associated with the offshore wind power generator in the system. The method according to claim 1,
Wherein the main controller of the power conversion apparatus controls the power conversion apparatus constituting the output voltage and the output current of the power conversion apparatus by a multi-level pulse width modulation method. The method of claim 4,
After the providing step,
And compensating for the reactive power by performing power conversion by the multi-level pulse width modulation method based on the value for reactive power compensation provided from the main controller of the power generator by the power inverter main controller. A method for compensating reactive power of an offshore wind turbine. 1. An offshore wind power generation system for providing power generated by an offshore wind power generator to a system via a High Voltage Alternating Current (HVAC)
And a controller for receiving the voltage and current of the grid associated with the offshore wind turbine monitored from the inverter of the power conversion apparatus and determining whether the voltage of the received grid is below a predetermined grid reference voltage, A power converter main controller for externally supplying the voltage and current of the received system when the voltage is less than a predetermined system reference voltage; And
And calculates a reactive power value using the voltage and current of the system provided from the main controller of the power conversion apparatus, compares the calculated reactive power value with a predetermined reactive power reference value, and calculates a difference between the calculated reactive power value and the reactive power reference value And a wind power generator main controller for providing a reactive power compensation value to the main controller of the power conversion system. The method of claim 6,
Wherein the main controller of the power conversion apparatus controls the power conversion apparatus that constitutes an output voltage and an output current of the power conversion apparatus by a multi-level pulse width modulation scheme. The method of claim 7,
Wherein the main controller of the power conversion apparatus performs power conversion based on the value for the reactive power compensation using the multi-level pulse width modulation scheme to compensate the reactive power.

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