초록 ▼

The present invention provides_a power converter that can be used to interface a generator (4) that provides variable voltage at variable frequency to a supply network operating at nominally fixed voltage and nominally fixed frequency and including features that allow the power converter to remain c

The present invention provides_a power converter that can be used to interface a generator (4) that provides variable voltage at variable frequency to a supply network operating at nominally fixed voltage and nominally fixed frequency and including features that allow the power converter to remain connected to the supply network and retain control during supply network fault and transient conditions. The power converter includes a generator bridge (10) electrically connected to the stator of the generator (4) and a network bridge (14). A dc link (12) is connected between the generator bridge (10) and the network bridge (14). A filter (16) having network terminals is connected between the network bridge (14) and the supply network. A first controller (18) is provided for controlling the operation of the semiconductor power switching devices of the generator bridge (14). Similarly, a second controller (46) is provided for controlling the operation of the semiconductor power switching devices of the network bridge (14). The first controller (18) uses a dc link voltage demand signal (VDC13 GEN*) indicative of a desired dc link voltage to control the semiconductor power switching devices of the network bridge (10) to achieve the desired level of dc link voltage that corresponds to the dc link voltage demand signal (VDC13 GEN*). The second controller (46) uses a power demand signal (P*) indicative of the level of power to be transferred from the dc link to the supply network through the network bridge (14), and a voltage demand signal (VTURB*) indicative of the voltage to be achieved at the network terminals of the filter (16) to control the semiconductor power switching devices of the network bridge (14) to achieve the desired levels of power and voltage that correspond to the power and voltage demand signals (P* and VTURB*).

대표청구항 ▼

What is claimed is: 1. A power converter that can be used to interface a generator that provides variable voltage at variable frequency to a supply network operating at nominally fixed voltage and nominally fixed frequency, the power converter comprising: a first active rectifier/inverter electrica

What is claimed is: 1. A power converter that can be used to interface a generator that provides variable voltage at variable frequency to a supply network operating at nominally fixed voltage and nominally fixed frequency, the power converter comprising: a first active rectifier/inverter electrically connected to the stator of the generator and including a plurality of semiconductor power switching devices; a second active rectifier/inverter including a plurality of semiconductor power switching devices; a dc link connected between the first active rectifier/inverter and the second active rectifier/inverter; a filter connected between the second active rectifier/inverter and the supply network, the filter including network terminals; a first controller for the first active rectifier/inverter; and a second controller for the second active rectifier/inverter: wherein the first controller uses a dc link voltage demand signal indicative of a desired dc link voltage to control the semiconductor power switching devices of the first active rectifier/inverter to achieve the desired level of dc link voltage that corresponds to the dc link voltage demand signal; and wherein the second controller uses a power demand signal indicative of the level of power to be transferred from the dc link to the supply network through the second active rectifier/inverter, and a voltage demand signal indicative of the voltage to be achieved at the network terminals of the filter to control the semiconductor power switching devices of the second active rectifier/inverter to achieve the desired levels of power and voltage that correspond to the power and voltage demand signals. 2. The power converter according to claim 1, wherein the first controller uses a flux demand signal indicative of a desired level of flux to be achieved in the generator, converts the flux demand signal to a direct axis current demand signal for the first active rectifier/inverter and controls the semiconductor power switching devices of the first active rectifier/inverter to produce stator electrical quantities that achieve the desired direct axis current for the first active rectifier/inverter. 3. The power converter according to claim 2, wherein the first controller converts the flux demand signal to the direct current axis demand signal with reference to one or more characteristics of the generator. 4. The power converter according to claim 2, wherein the first controller compares the dc link voltage demand signal indicative of a desired dc link voltage to a dc link voltage feedback signal to determine a quadrature axis current demand signal for the first active rectifier/inverter and controls the semiconductor power switching devices of the first active rectifier/inverter to produce stator electrical quantities that achieve the desired quadrature axis current for the first active rectifier/inverter. 5. The power converter according to claim 4, wherein the second controller supplies a control signal that varies in accordance with the prevailing supply network voltage conditions to the first controller, and wherein the first controller compares the dc link voltage demand signal indicative of a desired dc link voltage to the dc link voltage feedback signal to determine a dc link current demand signal, limits the dc link current demand signal using the control signal from the second controller to determine a limited dc link current demand signal and uses the limited dc link current demand signal to determine the quadrature axis current demand signal for the first active rectifier/inverter. 6. The power converter according to claim 4, wherein the second controller supplies a control signal that varies in accordance with the prevailing supply network voltage conditions and/or the power demand signal to the first controller, and wherein a dc link voltage controller of the first controller compares the dc link voltage demand signal indicative of a desired dc link voltage to the dc link voltage feedback signal to provide an output signal that is added to the control signal to determine a dc link current demand signal that is used to determine the quadrature axis current demand signal for the first active rectifier/inverter. 7. The power converter according to claim 4, wherein the second controller converts the power demand signal indicative of the level of power to be transferred from the dc link to the supply network through the second active rectifier/inverter to a quadrature axis current demand signal for the second active rectifier/inverter and controls the semiconductor power switching devices of the second active rectifier/inverter to produce filter/supply network electrical quantities that achieve the desired quadrature axis current for the second active rectifier/inverter. 8. The power converter according to claim 7, wherein the power demand signal is converted into the quadrature axis current demand signal by dividing the power demand signal by a signal that is derived from the voltage at the network terminals of the filter. 9. The power converter according to claim 7, wherein the power demand signal is converted into the quadrature axis current demand signal by dividing the power demand signal by a filtered version of the signal that is derived from the voltage at the network terminals of the filter. 10. The power converter according to claim 7, wherein the second controller uses a further dc link voltage demand signal indicative of a desired dc link voltage, compares the further dc link voltage demand signal to the dc link voltage feedback signal to determine an unlimited quadrature axis current demand signal and limits the unlimited quadrature axis current demand signal to a value determined by a limiting signal that is derived from the power demand signal to determine the quadrature axis current demand signal for the second active rectifier/inverter. 11. The power converter according to claim 10, wherein the unlimited quadrature axis current demand signal is added to a quadrature axis current feedforward signal that is derived from: (i) a signal indicative of the generator power, (ii) a voltage feedback signal measured at the network terminals of the filter and (iii) a gain signal that varies in accordance with the prevailing supply network voltage conditions. 12. The power converter according to claim 11, wherein the signal indicative of the generator power is supplied to the second controller from the first controller. 13. The power converter according to claim 11, wherein the signal indicative of the generator power minus the output of a PI controller of a dc link voltage controller of the first controller is supplied to the second controller and is used by the second controller only during a supply voltage dip situation. 14. The power converter according to claim 10, wherein the second controller modifies the limiting signal that is derived from the power demand signal in accordance with the prevailing supply network voltage conditions. 15. The power converter according to claim 1, wherein the dc link includes a capacitor and the power converter further comprises a current sensor for measuring the current flowing in the capacitor and providing an output signal. 16. The power converter according to claim 14, wherein the output signal of the current sensor is subtracted from a signal derived from a signal indicative of the generator power to provide a signal that is added to the output of a dc link voltage controller of the first controller to determine a dc link current demand signal for the first active rectifier/inverter. 17. The power converter according to claim 14, wherein the output signal of the current sensor is subtracted from a signal derived from a signal indicative of the generator power to provide a signal that is filtered and added to the output of a dc link voltage controller of the first controller to determine a dc link current demand signal for the first active rectifier/inverter. 18. The power converter according to claim 1, further comprising a voltage sensor for measuring the dc link voltage and providing a dc link voltage feedback signal and means for measuring the rate of change of the dc link voltage feedback signal, wherein the integral value of a PI controller of a dc link voltage controller of the first controller is modified by a predetermined factor when the dc link voltage feedback signal is greater than a first threshold and the rate of change of the dc link voltage feedback signal is greater than a second threshold. 19. The power converter according to claim 1, wherein during a supply network voltage dip situation, a quadrature axis current axis demand signal for the second active rectifier/inverter is derived from a slew rate limited version of a signal derived from the power limit rating of the second active rectifier/inverter that is modified as a function of the prevailing supply network voltage conditions. 20. The power converter according to claim 1, wherein the second controller compares the voltage demand signal indicative of the level of voltage to be achieved at the network terminals of the filter to a voltage feedback signal measured at the network terminals of the filter to determine a direct axis current demand signal for the second active rectifier/inverter and controls the semiconductor power switching devices of the second active rectifier/inverter to produce filter/supply network electrical quantities that achieve the desired direct axis current for the second active rectifier/inverter. 21. The power converter according to claim 20, wherein the second controller modifies the direct axis current demand signal in accordance with the prevailing supply network voltage conditions. 22. The power converter according to claim 20, wherein the second controller modifies an error signal arising from the difference between the voltage demand signal indicative of the level of voltage to be achieved at the network terminals of the filter and the voltage feedback signal measured at the network terminals of the filter in accordance with a signal derived from the direct axis current demand signal. 23. The power converter according to claim 1, further comprising a speed sensor or speed observer for deriving a speed signal indicative of the speed of the moving part of the generator and wherein the speed signal is used to derive the power demand signal. 24. The power converter according to claim 23, wherein the power demand signal is derived from a look-up table or mathematical function and the speed signal forms a pointer to the look-up table or a value for which the mathematical function is calculated. 25. The power converter according to claim 23, wherein the speed signal is modified by a filter function. 26. The power converter according to claim 25, wherein the power demand signal is derived from a look-up table or mathematical function and the modified speed signal forms a pointer to the look-up table or a value for which the mathematical function is calculated. 27. The power converter according to claim 23, wherein the power demand signal is summed with a signal derived from a filtered version of tile speed signal. 28. An arrangement comprising a plurality of power converters each including: a first active rectifier/inverter electrically connected to the stator of the generator and including a plurality of semiconductor power switching devices; a second active rectifier/inverter including a plurality of semiconductor power switching devices; a dc link connected between the first active rectifier/inverter and the second active rectifier/inverter; a filter connected between the second active rectifier/inverter and the supply network, the filter including network terminals; a first controller for the first active rectifier/inverter; and a second controller for the second active rectifier/inverter; wherein the first controller uses a dc link voltage demand signal indicative of a desired dc link voltage to control the semiconductor power switching devices of the first active rectifier/inverter to achieve the desired level of dc link voltage that corresponds to the dc link voltage demand signal; and wherein the second controller uses a power demand signal indicative of the level of power to be transferred from the dc link to the supply network through the second active rectifier/inverter, and a voltage demand signal indicative of the voltage to be achieved at the network terminals of the filter to control the semiconductor power switching devices of the second active rectifier/inverter to achieve the desired levels of power and voltage that correspond to the power and voltage demand signals; the power converters being connected together in parallel to a supply network operating at nominally fixed voltage and nominally fixed frequency by a parallel connection, wherein the voltage demand signal indicative of the voltage to be achieved at the network terminals of the filter of each power converter is derived from a comparison of a top-level voltage demand signal and a top-level voltage feedback signal that is measured at the point where the parallel connection is connected to the supply network. 29. The arrangement according to claim 28, wherein each individual power converter includes a step-up transformer electrically connected between the associated filter and the parallel connection. 30. The arrangement according to claim 28, further comprising a step-up transformer electrically connected between the parallel connection and the supply network. 31. The arrangement according to claim 30, wherein the top-level voltage feedback signal is measured at the supply network side of the step-up transformer electrically connected between the parallel connection and the supply network. 32. The arrangement according to claim 30, wherein the top-level voltage feedback signal is measured at the parallel connection side of the step-up transformer electrically connected between the parallel connection and the supply network.