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 (VDC_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 (VDC_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 method of operating 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 rectif

What is claimed is: 1. A method of operating 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 method comprises the steps of: the first controller using 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 the second controller using 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 method according to claim 1, further comprising the step of the second controller using a measure of the supply network voltage to determine limits on the power that can be exported from the second active rectifier/inverter when the supply network voltage deviates from its nominal condition. 3. The method according to claim 1, further comprising the step of the second controller using a measure of the supply network voltage to determine the level of current that is to be provided from the second active rectifier/inverter to provide voltage support to the supply network when the supply network voltage deviates from its nominal condition. 4. The method according to claim 1, further comprising the step of the first controller using a flux demand signal indicative of a desired level of flux to be achieved in the generator, converting the flux demand signal to a direct axis current demand signal or the first active rectifier/inverter and controlling 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. 5. The method according to claim 4, wherein the step of converting the flux demand signal to the direct current axis demand signal is carried out with reference to one or more characteristics of the generator. 6. The method according to claim 1, further comprising the step of the first controller comparing 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 controlling 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. 7. The method according to claim 6, further comprising the steps of: the second controller supplying a control signal that varies in accordance with the prevailing supply network voltage conditions to the first controller during a supply network voltage dip situation; and the first controller comparing 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 limiting the dc link current demand signal using the control signal from the second controller to determine a limited dc link current demand signal and using the limited dc link current demand signal to determine the quadrature axis current demand signal for the first active rectifier/inverter so that no power is drawn from the supply network during the supply network voltage dip situation. 8. The method according to claim 6, further comprising the steps of the second controller supplying 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 a dc link voltage controller of the first controller comparing 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. 9. The method according to claim 6, further comprising the step of the second controller converting 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 controlling 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. 10. The method according to claim 9, wherein the step of converting the power demand signal to the quadrature axis current demand signal is carried out by dividing the power demand signal by a signal that is derived from the voltage at the network terminals of the filter. 11. The method according to claim 10, wherein the step of converting the power demand signal into the quadrature axis current demand signal is carried out 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. 12. The method according to claim 9, further comprising the step of the second controller using a further dc link voltage demand signal indicative of a desired dc link voltage, comparing the further dc link voltage demand signal to the dc link voltage feedback signal to determine an unlimited quadrature axis current demand signal and limiting 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 during start-up and the normal operating condition of the power converter. 13. The method according to claim 12, further comprising the step of adding the unlimited quadrature axis current demand signal 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. 14. The method according to claim 13, wherein the signal indicative of the generator power is supplied to the second controller from the first controller. 15. The method according to claim 13, 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. 16. The method according to claim 12, further comprising the step of the second controller modifying the limiting signal that is derived from the power demand signal in accordance with the prevailing supply network voltage conditions in a supply network voltage dip situation. 17. The method 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 the method further comprising the steps of subtracting the output signal of the current sensor 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. 18. The method 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, the method further comprising the steps of subtracting the output signal of the current sensor 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. 19. The method according to claim 1, wherein the power converter further comprises 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, the method further comprising the steps of modifying the integral value of a PI controller of a dc link voltage controller of the first controller 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. 20. The method according to claim 1, further comprising the step of deriving a quadrature axis current axis demand signal for the second active rectifier/inverter 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 in a supply network voltage dip situation. 21. The method according to claim 1, further comprising the step of the second controller comparing 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 controlling 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. 22. The method according to claim 21, further comprising the step of the second controller modifying the direct axis current demand signal in accordance with the prevailing supply network voltage conditions. 23. The method according to claim 21, further comprising the step of the second controller modifying 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. 24. The method according, to claim 1, further comprising the step of deriving a speed signal indicative of the speed of the moving part of the generator and using the speed signal to derive the power demand signal. 25. The method according to claim 24, further comprising the step of deriving the power demand signal from a look-up table or mathematical function where the speed signal forms a pointer to the look-Lip table or a value for which the mathematical function is calculated. 26. The method according to claim 24, further comprising the step of modifying the speed signal by a filter function. 27. The method according to claim 26, further comprising the step of deriving the power demand signal from a look-up table or mathematical function where the modified speed signal forms a pointer to the look-up table or a value for which the mathematical function is calculated. 28. The method according to claim 24, further comprising the step of summing the power demand signal with a signal derived from a filtered version of the speed signal. 29. A method of operating 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, the method comprising the step of deriving the voltage demand signal indicative of the voltage to be achieved at the network terminals of the filter of each power converter 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. 30. The method according to claim 29, further comprising the step of measuring the top-level voltage feedback signal at the supply network side of the step-up transformer electrically connected between the parallel connection and the supply network. 31. The method according to claim 29, further comprising the step of measuring the top-level voltage feedback signal at the parallel connection side of the step-up transformer electrically connected between the parallel connection and the supply network.