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Patent Issued for Method For Operating A Wind Turbine (USPTO 10,727,843)

Source: 
Engineering Business Daily

2020 AUG 11 (NewsRx) -- By a News Reporter-Staff News Editor at Engineering Business Daily -- Woodward Kempen GmbH (Kempen, Germany) has been issued patent number 10,727,843, according to news reporting originating out of Alexandria, Virginia, by NewsRx editors.

The patent’s inventors are Schall, Nils-Hendric (Berlin, DE); Genius, Andreas (Muelheim an der Ruhr, DE); Hoffmann, Nils (Halle/Saale, DE).

This patent was filed on January 18, 2019 and was published online on August 10, 2020.

From the background information supplied by the inventors, news correspondents obtained the following quote: “The present invention relates to a method for operating a wind turbine, which supplies, synchronized with a network voltage, electrical power to an electrical power supply network via a converter.

“In general, the invention relates to the field for the control of a converter system of a wind turbine, in particular the control of a partial converter for a double-fed asynchronous generator. For operating the wind turbine, the control of the converter in the event of a network failure presents a special technical challenge.

“A method and a device for operating an electrical machine are known from EP 1 914 877 A2. The electrical machine, which may be a wind turbine, is designed to be connected electrically with the electrical power supply network. A controller is provided for the electrical machine so that it remains connected electrically with the power supply network during and after a voltage drop for an indeterminate period of time. In particular, it is known to provide a phase locked loop, which has a phase detector and at least one proportional integral (PI) filter, in the event of a drop in voltage to almost zero volts, zero voltage ride through (ZVRT). It is further provided that the parameters of the PI filter can be selected discretely depending on states defined depending on the network voltage, wherein a state machine can be accessed for this.

“It is known from U.S. Pat. No. 6,941,113 B2 to control a wind turbine with a double-fed asynchronous generator via a phase locked loop. In the event of certain events in the network and/or in the wind turbine, it can happen that the phase locked loop is temporarily not synchronous with the network voltage. The phase locked loop in this case permits the wind turbine to ride through the event and only supply power again at a later point in time synchronously with the network voltage. So that the phase locked loop can be synchronized again quickly, a phase angle deviation is determined and a scaling factor is calculated from it when a minimum value is exceeded, which is applied to the setpoint values of the currents to be supplied.

“The object of the invention is to provide a method for operating a wind turbine, which permits with simple means even in the case of transient voltage errors in the electrical power supply network a reliable and dynamic tracking of the phase angle and thereby avoids erratic behavior. Furthermore, a method should be specified that permits stable operation of the wind turbine over the entire voltage range.”

Supplementing the background information on this patent, NewsRx reporters also obtained the inventors’ summary information for this patent: “The method according to the invention is provided and determined for operating a wind turbine, which supplies, synchronized with a network voltage, electrical power to an electrical power supply network via a converter. For example, this can be a wind turbine equipped with a double-fed asynchronous machine, which supplies power via a partial converter. The method according to the invention accesses a phase angle measured in the electrical power supply network and a voltage measured in it. The supplying of electrical power set in its phase position for the network voltage and its phase takes place via a phase locked loop, at which the measured phase angle from the electrical power supply is present and which outputs a corrected phase angle for controlling the converter. In the method according to the invention, at least one parameter of the phase locked loop is determined depending on the measured amplitude value of the voltage in the electrical power supply. This makes it possible to determine the behavior of the phase locked loop in a voltage-dependent manner and to adjust the at least one parameter on the phase locked loop. In this manner, the behavior of the phase locked loop is set in a voltage-dependent manner and can thus be adjusted well for a voltage drop in the network without the phase locked loop changing its dynamics for regular operation. The invention enables a riding through of a deep network voltage error, wherein the wind turbine remains connected with the network and without thereby negatively impacting the control dynamics of the phase locked loop in the rated operation of the wind turbine. If for example high dynamics are desired in the case of the power supply of the wind turbine relative to network frequency oscillations for the rated operation of the wind turbine, then this does not collide with a large inertia of the phase locked loop in the case of a voltage drop, in particular not in the case of a voltage drop from zero volts or almost zero volts, zero voltage ride through (ZVRT).

“In an embodiment, the at least one parameter, which is determined in a voltage-dependent manner, is selected such that it determines the dynamics of the phase locked loop. The voltage dependency is hereby selected such that, for example in the case of a low measured voltage, the dynamics of the phase locked loop is adjusted. It is hereby possible to adjust the dynamics of the phase locked loop in a voltage-dependent manner as needed. For example, both a highly dynamic operation of the phase locked loop in regular operation as well as operation with slowed dynamics in the event of a voltage drop are thereby possible.

“In an embodiment, in the case of a measured voltage below a threshold value, the at least one parameter will assume a value with which the phase locked loop holds constant the last corrected phase angle. The phase locked loop freezes at a constant value which was present at the converter as the corrected phase angle before the voltage drop. The threshold value can thereby be preferably set or parameterized by selecting the function/characteristic curve.

“In general, the phase locked loop can be structured in any manner for the present invention. It is particularly advantageous to provide a proportional loop filter with an amplification factor K.sub.P. The value of the amplification factor K.sub.P is determined in a voltage-dependent manner. The dynamics of the phase locked loop can be determined in a voltage-dependent manner from the proportionality constant K.sub.P and/or the time constant T.sub.1.

“The phase-locked loop preferably has a feed-forward control of the network frequency, which has a low-pass filter with a time constant T.sub.1, the value of which is determined in a voltage-dependent manner.

“The time constant T.sub.1 is increased to a very high value in the event of a network error so that the phase locked loop outputs an almost constant value for the corrected phase angle.

“The amplification factor K.sub.P is reduced to a value of approximately zero in the event of a network error so that the phase locked loop outputs an almost constant value for the corrected phase angle.

“One or several different criteria can be defined for the network error. A criterion for a particularly strong voltage drop is then present when the voltage drops to a value below a threshold value. This scenario also comprises a voltage drop to zero and to almost zero volts, in the case of which the network voltage fails.

“The at least one parameter is preferably continuously dependent on the voltage. A value for the parameter is thus continuously assigned to each voltage value between a voltage value in the event of the network error and the nominal voltage or even beyond, wherein in the case of the network error a constant value is set for the corrected phase angle and in the case of the nominal voltage a predetermined dynamic is set for the phase locked loop. The at least one parameter preferably progresses continuously between a minimum and a maximum value, for example in the form of a saturation curve. In an embodiment, the value of the at least one parameter assumes its values proportionally, preferably approximately linearly between two turning points, depending on the voltage value.”

The claims supplied by the inventors are:

“The invention claimed is:

“1. A method for operating a wind turbine configured to supply electrical power to an electrical power supply network via a converter, the method comprising: measuring a phase angle and measuring a voltage of the electrical power supply network; determining a value of at least one parameter for a phase locked loop depending on the measured voltage; adjusting for a network error, wherein the network error comprises a voltage drop to a value of 15% of nominal value or less; using the phase locked loop to determine a corrected phase angle depending on the measured phase angle and the measured voltage of the electrical power supply network; and inputting the corrected phase angle into the converter.

“2. The method according to claim 1, wherein the at least one parameter determines dynamics of the phase locked loop.

“3. The method according to claim 2, wherein the at least one parameter is configured to slow the dynamics if the measured voltage is low.

“4. The method according to claim 3, wherein the at least one parameter assumes a value such that the phase locked loop holds the corrected phase angle at an almost constant value if the measured voltage is below a threshold value.

“5. The method according to claim 1, further comprising a proportional loop filter, wherein the at least one parameter is a proportionality constant K.sub.P, and wherein a value of the proportionality constant is determined in a voltage-dependent manner.

“6. The method according to claim 5, further comprising a low-pass filter, wherein the at least one parameter is a time constant T.sub.1, and wherein a value of time constant is determined in a voltage-dependent manner.

“7. The method according to claim 6, wherein dynamics of the phase locked loop are determined in a voltage-dependent manner by at least one of the proportionality constant Kp and the time constant T.sub.1.

“8. The method according to claim 6, wherein the proportionality constant K.sub.P assumes a value of almost zero when there is a network error.

“9. The method according to claim 8, wherein the value of the time constant T.sub.1 is considerably increased when there is a network error.

“10. The method according to claim 6, further comprising a dead-time element having an adjustable dead time Tt.

“11. The method according to claim 1, wherein the at least one parameter is specified as a continuous function depending on the voltage.

“12. The method according to claim 11, wherein the value of the at least one parameter progresses in a voltage-dependent manner between a minimum value and a maximum value.

“13. The method according to claim 1, wherein the voltage is a positive sequence voltage.

“14. The method according to claim 1, wherein the voltage is a negative sequence voltage.

“15. The method according to claim 1, wherein the corrected phase angle is determined in a continuous manner.

“16. The method according to claim 1, further comprising setting the at least one parameter of the phase locked loop.”

For the URL and additional information on this patent, see: Schall, Nils-Hendric; Genius, Andreas; Hoffmann, Nils. Method For Operating A Wind Turbine. U.S. Patent Number 10,727,843, filed January 18, 2019, and published online on August 10, 2020. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=10,727,843.PN.&OS=PN/10,727,843RS=PN/10,727,843

 

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