Abstract:
A method for islanding detection in an electrical power grid (18) supplied by an electrical power source (12) comprises: measuring an output voltage ( V pcc ) and a grid current ( I g ) at an interconnection point (16) of the power source (12) with the power grid (18); estimating at least one grid parameter from the output voltage ( V pcc ) and the grid current ( I g ) based on optimizing a cost function, which minimizes a difference between the measured output voltage( V pcc ) and an estimated output voltage or a difference between the measured grid current ( I g ) and an estimated grid current, which estimated output voltage or estimated output current is a function of the measured grid current ( I g ) or the measured output voltage ( V pcc ) and the least one estimated grid parameter; and detecting an islanding condition by detecting a jump (32) and/or a deviation (34) in the at least one estimated grid parameter.
Abstract:
The invention relates to a power generation system, comprising a synchronous generator (3) for converting mechanical power into electrical power at an output side configured for connecting an AC power grid (1), a first rectifier (12) and a second rectifier (13) each having an AC side (14) connected to the output side of the generator (3) and a DC side (15), an exciter (9) configured for exciting the, and a selector device (18) having an input side (17) and an output side (19), the input side (17) connected to the DC side (15) of the first rectifier (12) and to the DC side (15) of the second rectifier (13) and the output side (19) connected to the exciter (9), whereby the selector device (18) is configured for switching the DC sides (15) in series or in parallel or for transmitting DC power from the first rectifier (12) and the second rectifier (13) corresponding to an arbitrary split ratio to the output side (19).
Abstract:
A synchronous machine (12) comprises a stator (22) with stator windings (18) connected with stator terminals (20) to an electrical grid (16) and a rotor (24) with rotor windings (26) rotatable mounted in the stator (22), wherein a voltage regulator (14) of the synchronous machine (12) is adapted for outputting an excitation signal ( u ) to adjust a current in the rotor windings (26) for controlling the synchronous machine (12). A method for determining control parameters (54) for the voltage regulator (14) comprises: receiving a first time series of values of the excitation signal ( u ) and a second time series of measurement values of a terminal voltage ( y ) in the stator terminals (20), wherein the first time series and the second time series are acquired over a time interval; determining coefficients (52) of a system transfer function ( G(s) ) of the synchronous machine (12), wherein the system transfer function (G(s j) is a rational function, wherein the coefficients (52) of the system transfer function ( G(s) ) are determined recursively with a regression analysis with instrumental variables based on the first time series as system input and the second time series as system output; and determining the control parameters (54) for the voltage regulator (14) from the coefficients (52) of the system transfer function ( G(s) ) by comparing a closed loop transfer function formed of a controller transfer function ( C(s) ) of the voltage regulator (14) and the system transfer function ( G(s) ) with a desired closed loop transfer function.
Abstract:
A method for controlling a three-phase electrical converter (12) comprises: selecting a three-phase optimized pulse pattern (20) from a table (22) of precomputed optimized pulse patterns based on a reference flux (ψ αβ,ref ); determining a two-component optimal flux {ψ* αβ ) from the optimized pulse pattern (20) and determine a one-component optimal third variable (ζ*); determining a two-component flux error from a difference of the optimal flux ( ψ* αβ ) and an estimated flux (ψ αβ ) estimated based on measurements in the electrical converter; determining a one-component third variable error from a difference of the optimal third variable (ζ*) and an estimated third variable (ζ); modifying the optimized pulse pattern (20) by time-shifting switching instants (28) of the optimized pulse pattern (20) such that a cost function depending on the time-shifts is minimized, wherein the cost function comprises a flux error term and a third variable error term, wherein the flux error term is based on a difference of the flux error and a flux correction function providing a flux correction based on the time-shifts and the third variable error term is based on a difference of the third variable error and a third variable correction function providing a third variable correction based on the time-shifts; and applying the modified optimized pulse pattern (26) to the electrical converter (12).
Abstract:
A method for estimating an equivalent impedance (Z eq ) of a power grid (18) comprises: measuring a plurality of measurement values of a generator voltage (V gen ) and a generator current (I gen ) of at least one generator (12) connected to the power grid (18); generating a performance index (J) from the plurality of measurement values, the performance index being a function of the measurement values and the grid impedance (Z eq ); and determining an equivalent impedance (Z eq ) as the grid impedance, which minimizes the performance index (J). The performance index (J) is additionally a function of an angular error (δ), which accounts for a deviation of a grid frequency at a measurement of a measurement value from a nominal grid frequency, and the performance index (J) is additionally minimized with respect to the angular error (δ).
Abstract:
A method for estimating a fundamental component (A) of an AC voltage ( V pcc ) comprises: receiving a timely varying measurement signal of the AC voltage ( V pcc ); parametrizing a fundamental component (A) of the AC voltage ( V pcc ), the fundamental component (A) having a rated frequency, a variable amplitude and a variable phase shift; and determining parameters (B) of the fundamental component (A) based on minimizing a cost function ( J ), wherein the cost function ( J ) is based on an integral of a norm of a difference between the measurement signal and the parametrized fundamental component via a time horizon (h ), the time horizon ( h ) starting at an actual time point and going back via a predefined length. The cost function ( J ) comprises a term based on a norm of the difference between a value of the fundamental component ( ) at the actual time point and a value of a previously estimated fundamental component ( ) at the actual time point, whereby the previously estimated fundamental component has been determined for a previous time point.
Abstract:
A method for operating an electrical converter (12) comprises: determining an optimized pulse pattern (I) from a fundamental voltage reference (II) for the electrical converter (12), wherein the optimized pulse pattern (I) is determined from a first lookup table (30) and comprises discrete voltage amplitude values changing at predefined switching instants (24); determining a harmonic content reference (III) from the fundamental voltage reference (II) based on a second lookup table (34), wherein the harmonic content reference is a harmonic current reference (IV) determined from the frequency spectrum of a current of the electrical converter (12) or the harmonic content reference is a filtered voltage reference (V) determined by applying a first order frequency filter to a voltage, which current or voltage is generated, when the optimized pulse pattern is applied to the electrical converter (12); determining a harmonic content error (VI) from the harmonic content reference (III) by subtracting an estimated output voltage ( ψ(t) ) and/or estimated output current ( i(t) ) of the electrical converter (12) from the harmonic content reference (III); modifying the optimized pulse pattern (I) by timeshifting switching instants (24) such that the fundamental voltage reference (II) is tracked and the harmonic content error (VI) is corrected by the timeshifted switching instants (24); applying the modified optimized pulse pattern ( v(t) ) to semiconductor switches of the electrical converter (12).
Abstract:
An electrical converter (12) comprises at least one of an active rectifier (20) and an inverter (22) interconnecting an electrical source (16) with an electrical load (18). A method for controlling an electrical converter (12) comprises: receiving at least one estimated control variable (38), which is estimated from measurement values measured in the electrical converter (12); receiving at least one outer loop control variable (36) provided by an outer control loop, the at least one outer loop control variable providing a desired steady-state operation point of the electrical converter (12); determining a control region (56a, 56b) based on a control error, which is a difference between the at least one estimated control variable (38) and the at least one outer loop control variable (36), wherein the control region is defined by one or more intervals of one or more control variables; selecting control parameters based on the control region (56a, 56b), wherein, when the control error is in an inner control region (56a), first control parameters are selected, and, when the control error is outside the inner control region but inside an outer control region (56b), second control parameters are selected; switching, based on the control error, between two and more control methods, which differ in control parameters, by predicting at least one reference control value (40) based on a solution (50) of a physical model (44) of the electrical converter (12), which comprises the selected control parameters, the physical model (44) being based on differential equations modelling the at least one estimated control variable (38) and the solution (50) being based on a constraint minimizing a difference between the at least one estimated control variable (38) and the at least one outer loop control variable (36); and determining switching states (42) of the electrical converter (12) based on the reference control value (40).