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Processor-based field oriented control for brushless doubly-fed induction machine having first and second polyphase stator windings is programmed to operate the machine in various modes, as a motor or a generator, with bumpless switching between operating modes. An electronic power converter control

Processor-based field oriented control for brushless doubly-fed induction machine having first and second polyphase stator windings is programmed to operate the machine in various modes, as a motor or a generator, with bumpless switching between operating modes. An electronic power converter controls a current supplied to the first stator winding to control the torque of the machine, with the second stator winding selectively connected to an AC line. Stationary coordinates for in-phase and quadrature current commands are coordinate transformed using a voltage vector for voltage induced on the first polyphase stator winding to control current in the first stator winding, with or without a position sensor. The electronic power converter controls the voltage supplied to the first stator for generating, with the second stator selectively connected to a load. The machine can also be controlled to operate as a singly-fed motor at lower speeds, with the second stator winding shorted.

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1. A method of field oriented control for substantially independently controlling an excitation current and a torque producing current of a doubly-fed induction machine having a first polyphase stator winding and a second polyphase stator winding that are substantially electrically and magnetically

1. A method of field oriented control for substantially independently controlling an excitation current and a torque producing current of a doubly-fed induction machine having a first polyphase stator winding and a second polyphase stator winding that are substantially electrically and magnetically independent, and a brushless induction rotor assembly that magnetically couples the first and the second polyphase stator windings in a reverse phase sequence, wherein a desired excitation current and a desired torque producing current in one polyphase stator winding are defined in stationary coordinates by a quadrature current command and an in-phase current command, respectively, the method comprising the steps of:(a) coupling the first polyphase stator winding to a polyphase electronic power converter having a power input connected to an alternating current (AC) line, and coupling the second polyphase stator winding to the AC line;(b) monitoring currents in at least two phases of the first polyphase stator winding and in at least one phase of the second polyphase stator winding;(c) monitoring a voltage of at least one phase of the AC line;(d) as a function of the currents that are monitored in step (b) and as a function of the voltage of the AC line monitored in step (c), calculating an angle of one of:(i) a voltage vector induced on the first polyphase stator winding by the AC line; and(ii) a flux vector in the first polyphase stator winding caused by the AC line, said flux vector lagging the voltage vector by 90 electrical degrees; and(e) coordinate transforming an in-phase command and a quadrature command, using the angle of step (d), to produce polyphase commands that are supplied to the polyphase electronic power converter, said polyphase commands causing the polyphase electronic power converter to maintain a torque producing component vector of the current in the first polyphase stator winding substantially proportional to the in-phase current command and substantially in one of a zero degree and a 180 degree relationship with the voltage vector of step (d), as required to produce a desired torque and to maintain an excitation component vector of current in the first polyphase stator winding substantially in quadrature with the voltage vector of step (d). 2. The method of claim 1, wherein the second polyphase stator winding is initially selectively not coupled to the AC line, further comprising the steps of:(a) synchronizing a voltage on the second polyphase stator winding with the voltage of the AC line; and then,(b) selectively coupling the second polyphase stator winding to the AC line. 3. The method of claim 1, wherein the polyphase electronic power converter is configured as a current regulator, current in the first polyphase stator winding is controlled, the quadrature current command is the quadrature command, the in-phase current command is the in-phase command, and the excitation component of the current in the first polyphase stator winding is substantially proportional to the quadrature current command. 4. The method of claim 1, wherein the polyphase electronic power converter is configured as an inverter, and current in the second polyphase stator winding is controlled, further comprising the steps of:(a) determining an in-phase current vector component and a quadrature current vector component, in stationary coordinates, for the second polyphase stator winding relative to the AC line;(b) as a function of a difference between the in-phase current command and the in-phase current vector component, determining the quadrature command for use in the coordinate transforming step;(c) as a function of a difference between the quadrature current command and the quadrature current vector component, determining the in-phase command for use in the coordinate transforming step; and(d) causing the excitation component of current in the first polyphase stator winding to be substantially inversely proportional to the quadratu re current command. 5. The method of claim 1, wherein the polyphase electronic power converter is configured as an inverter, and currents in the first polyphase stator winding are controlled, further comprising the steps of:(a) determining an in-phase current vector component and a quadrature current vector component in stationary coordinates for the first polyphase stator by coordinate transforming the current in the first polyphase stator winding by the angle of the voltage vector induced on the first polyphase stator winding;(b) as a function of a difference between the in-phase current command and the in-phase current vector component, determining the quadrature command for use in the coordinate transforming step of claim 1;(c) as a function of a difference between the quadrature current command and the quadrature current vector component, determining the in-phase command for use in the step of coordinate transforming of claim 1; and(d) causing the excitation component of current in the first polyphase stator winding to be substantially proportional to the quadrature current command. 6. The method of claim 3, further comprising the steps of:(a) determining an in-phase component of the current monitored in the second polyphase stator winding, relative to the AC line voltage; and(b) determining the in-phase current command as a function of a difference between a reference in-phase current command for the second polyphase stator winding and the in-phase component of the current monitored in the second polyphase stator winding. 7. The method of claim 3, further comprising the steps of:(a) determining a quadrature component of the current monitored in the second polyphase stator winding, relative to the AC line voltage; and(b) determining the quadrature current command as a function of a difference between a reference quadrature current command for the second polyphase stator winding and the quadrature component of the current monitored in the second polyphase stator winding. 8. The method of claim 1, wherein the step of calculating the angle of the voltage vector comprises the steps of:(a) determining an in-phase component for the current monitored in the second polyphase stator winding, which is in-phase relative to the AC line voltage;(b) multiplying the in-phase component thus determined by a current transformation ratio between the second polyphase stator winding and the first polyphase stator winding, to determine a component of a current in the first polyphase stator winding that is in-phase relative to the voltage vector;(c) determining a magnitude and an angle of a total current vector for the first polyphase stator winding;(d) determining a difference angle between a vector for the current that is in-phase in the first polyphase stator winding and the total current vector for the first polyphase stator winding; and(e) adding the angle of the total current vector in the first polyphase stator winding to the difference angle, to determine the angle of the voltage vector induced on the first polyphase stator winding. 9. The method of claim 1, further comprising the steps of:(a) sensing a rotational position of a shaft on which the brushless induction rotor assembly is mounted, producing a rotational position signal; and(b) determining a short term value for the angle of the voltage vector on the second polyphase stator winding as a function of the rotational position signal; and(c) correcting the short term value for the angle of the voltage vector with the angle of the voltage vector induced on the first polyphase stator winding by the AC line. 10. The method of claim 1, wherein the step of calculating the angle of the voltage vector comprises the steps of:(a) determining a vector sum of a current vector angle for currents in the first polyphase stator winding and in the second polyphase stator winding;(b) subtracting a vector angle for the voltage on the AC line from the vector sum to produce an uncorrected angle for t he voltage vector induced on the first polyphase stator winding; and(c) correcting the uncorrected angle of the voltage vector as a function of current in the second polyphase stator winding and the polyphase current commands, producing the angle of the voltage vector induced on the first polyphase stator winding by the AC line. 11. The method of claim 1, further comprising the step of controlling the quadrature current command to achieve a desired power factor for the second polyphase stator winding. 12. The method of claim 1, wherein the doubly-fed induction machine is employed as a motor, further comprising the steps of:(a) determining a rotational speed of the doubly-fed induction machine from the voltage and current that were monitored, producing a speed signal;(b) determining a difference between the speed signal and a desired rotational speed of the doubly-fed induction machine to determine a speed error; and(c) producing the in-phase current command as a function of the speed error. 13. The method of claim 1, wherein the second polyphase stator winding is initially selectively not coupled to the AC line, further comprising the steps of:(a) selectively shorting the second polyphase stator winding at rotational speeds of the doubly-fed induction machine less than a synchronous speed; and(b) selectively unshorting the second polyphase stator winding and selectively coupling the second polyphase stator winding to the AC line at rotational speeds of the doubly-fed induction machine that are above the synchronous speed, where the synchronous speed is a rotational speed of the doubly-fed induction machine at which a frequency of the first polyphase stator winding is equal to zero with the second polyphase stator winding selectively coupled to the AC line. 14. The method of claim 1, wherein the doubly-fed induction machine is employed as a generator, further comprising the steps of:(a) determining a rotational speed of the generator from the voltage and current that were monitored, producing a speed signal; and(b) producing the in-phase current command as a function of the speed signal to achieve a desired torque required to drive the generator. 15. The method of claim 1, wherein the doubly-fed induction machine is employed as a generator, and the second polyphase stator winding is initially selectively not coupled to the AC line, further comprising the steps of:(a) coupling the second polyphase stator winding to one side of a first open switch and to one side of a second open switch, another side of the first open switch being coupled to an alternating current (AC) line, and another side of the second open switch being coupled to an AC load;(b) enabling selective operation of the generator in one of a co-generation mode and a standalone mode;(c) when operation in the co-generation mode is selected:(i) monitoring one of:(1) voltages on each side of the first open switch, for at least one phase; and(2) a voltage across the first open switch, for at least one phase;(ii) prior to closing the first open switch and in response to said one of the voltages monitored in step (c)(i), automatically regulating one of a polyphase voltage and a polyphase current applied to the first polyphase stator winding by the electronic power converter so as to cause the voltage across the first open switch to approach a substantially zero value;(iii) automatically closing the first open switch when the voltage across the first open switch is substantially zero; and(iv) controlling a current supplied to the AC line by the machine, by controlling the polyphase current supplied to the first polyphase stator winding by the electronic power converter; and(d) when operation in the standalone mode is selected to energize the AC load:(i) controlling an output of the second polyphase stator winding with the electronic power converter, to attain a desired output; and(ii) then closing the second open switch to supply power to the load from the doubly-fed induct ion generator. 16. A field oriented control for a doubly-fed induction machine having a first polyphase stator winding and a second polyphase stator winding that are substantially electrically and magnetically independent, and a brushless induction rotor assembly that magnetically couples the first polyphase stator winding to the second polyphase stator winding in reverse phase sequence, said second polyphase stator winding being coupled to an alternating current (AC) line, comprising:(a) an electronic power converter adapted to couple to the first polyphase stator winding and to the AC line;(b) current inputs adapted to couple to current transducers that monitor currents in at least two phases of the first polyphase stator winding and in at least one phase of the second polyphase stator winding;(c) a voltage input adapted to couple to a voltage transducer that monitors a voltage of at least one phase of the AC line;(d) memory in which a plurality of machine instructions are stored; and(e) a processor coupled to the memory, said processor executing the machine instructions to cause the processor to carry out a plurality of functions, including:(i) calculating an angle of one of a voltage vector and a flux vector induced on the first polyphase stator winding by the AC line, as a function of the currents that are monitored by the current transducers and as a function of the voltage of the AC line monitored by the voltage transducer; and(ii) coordinate transforming an in-phase command and a quadrature command in stationary coordinates, using the angle of step (i), to produce polyphase commands that are supplied to the polyphase electronic power converter, said polyphase commands causing the polyphase electronic power converter to maintain a torque producing component vector of the current in the first polyphase stator winding substantially proportional to an in-phase current command and substantially in one of a zero degree and 180 degree relationship with the voltage vector of step (i), as required to produce a desired torque, and to maintain an excitation component vector of current in the first polyphase stator winding substantially in quadrature with the voltage vector of step (i). 17. The control of claim 16, further comprising an output that is adapted to operatively couple to a switch that is disposed between the second polyphase stator winding and the AC line and is initially open so that the second polyphase stator winding is initially not coupled to the AC line by the switch, the machine instructions further causing the processor to:(a) synchronize a voltage on the second polyphase stator winding with the voltage of the AC line; and then,(b) selectively close the switch to couple the second polyphase stator winding to the AC line. 18. The control of claim 16, wherein the machine instructions further cause the processor to:(a) configure the polyphase electronic power converter as a current regulator;(b) control current in the first polyphase stator winding;(c) employ the in-phase current command as the in-phase command and a quadrature current command as the quadrature command; and(d) maintain the excitation component of current in the first polyphase stator winding substantially proportional to the quadrature current command. 19. The control of claim 16, wherein the machine instructions further cause the processor to:(a) configure the polyphase electronic power converter as an inverter;(b) control current in the second polyphase stator winding;(c) define a desired excitation current and a desired torque producing current in the second polyphase stator winding in stationary coordinates, by a quadrature current command and the in-phase current command, respectively;(d) determine an in-phase current vector component and a quadrature current vector component, in stationary coordinates, for the second polyphase stator winding relative to the AC line;(e) as a function of a difference between the in-phase current command and t he in-phase current vector component, determine the quadrature command for use in coordinate transforming;(f) as a function of a difference between the quadrature current command and the quadrature current vector component, determining the in-phase command for use in coordinate transforming; and(g) maintain the excitation component of current in the first polyphase stator winding substantially inversely proportional to the quadrature current command. 20. The control of claim 16, wherein the machine instructions further cause the processor to:(a) configure the polyphase electronic power converter as an inverter;(b) control currents in the first polyphase stator winding;(c) define a desired excitation current and a desired torque producing current in the first polyphase stator winding by reference to a quadrature current command and the in-phase current command;(d) determine in-phase and quadrature current vector components in the first polyphase stator winding in stationary coordinates by coordinate transforming the current monitored in the first polyphase stator winding by the angle of the voltage vector induced on the first polyphase stator winding;(e) as a function of a difference between the in-phase current command and the in-phase current vector component, determine the quadrature command for use in coordinate transforming in claim 16(e)(ii);(f) as a function of a difference between the quadrature current command and the quadrature current vector component, determine the in-phase command for use in coordinate transforming in claim 16(e)(ii); and(g) maintain the excitation component of current in the first polyphase stator winding substantially proportional to the quadrature current command. 21. The control of claim 16, wherein the machine instructions further cause the processor to calculate the angle of one the voltage vector and the flux vector induced on the first polyphase stator winding by:(a) determining a magnitude of a vector for the current monitored in the second polyphase stator winding, which is in-phase relative to the AC line voltage;(b) multiplying the magnitude of the vector thus determined by a current transformation ratio between the second polyphase stator winding and the first polyphase stator winding, to determine a magnitude of a current in the first polyphase stator winding that is in-phase relative to the voltage vector;(c) determining a magnitude and an angle of a total current vector in the first polyphase stator winding;(d) determining a difference angle between a vector for the current that is in-phase in the first polyphase stator winding and the total current vector in the first polyphase stator winding; and(e) adding the angle of the total current vector in the first polyphase stator winding to the difference angle, to determine said one of the angle of the voltage vector and the flux vector induced on the first polyphase stator winding. 22. The control of claim 16, further comprising an input adapted to couple to a shaft position sensor that produces a rotational position signal for a rotational position of a shaft on which the brushless induction rotor assembly is mounted, the machine instructions further causing the processor to:(a) determine a short term value for the angle of one of the voltage vector and the flux vector as a function of the rotational position signal; and(b) correct the short term value for said angle with the angle that was calculated in claim 16(e)(i). 23. The control of claim 16, wherein the machine instructions cause the processor to calculate the angle of one of the voltage vector and the flux vector by:(a) determining a vector sum of a current vector angle for currents in the first polyphase stator winding and in the second polyphase stator winding;(b) subtracting a vector angle for the voltage on the AC line from the vector sum to produce an uncorrected angle for the voltage vector induced on the first polyphase stator winding; and(c) correcting the uncorrected angle of the voltage vector as a function of current in the second polyphase stator winding and the polyphase current commands, producing the angle of said one of the voltage vector and the flux vector induced on the first polyphase stator winding by the AC line. 24. The control of claim 16, wherein the machine instructions further cause the processor to control a quadrature current command that defines a desired excitation current to achieve a desired power factor for the second polyphase stator winding. 25. The control of claim 16, wherein the doubly-fed induction machine is employed as a speed controlled motor, and wherein the machine instructions further cause the processor to:(a) determine a rotational speed of the speed controlled motor from the voltage and the current that were monitored, producing a speed signal;(b) determine a difference between the speed signal and a desired rotational speed of the doubly-fed induction machine to determine a speed error; and(c) produce the in-phase current command as a function of the speed error. 26. The control of claim 16, further comprising an output that is adapted to operatively control a switch that is disposed between the second polyphase stator winding and the AC line, said switch being initially open so that the second polyphase stator winding is not coupled to the AC line by the switch; and, an output adapted to operatively control a shorting switch coupled to the second polyphase stator winding, the machine instructions further causing the processor to:(a) while the switch is initially open, selectively close the shorting switch to short the second polyphase stator winding at rotational speeds of the doubly-fed induction machine that are less than a synchronous speed; and(b) selectively open the shorting switch and selectively close the switch to couple the second polyphase stator winding to the AC line at rotational speeds of the doubly-fed induction machine that are above the synchronous speed, where the synchronous speed is a rotational speed of the doubly-fed induction machine at which a frequency of the first polyphase stator winding is equal to zero with the second polyphase stator winding selectively coupled to the AC line. 27. The control of claim 16, wherein the doubly-fed induction machine is employed as a generator, and wherein the machine instructions cause the processor to:(a) determine a rotational speed of the generator from the voltage and the current that were monitored, producing a speed signal; and(b) produce the in-phase current command as a function of the speed signal to achieve a desired torque required to drive the generator. 28. The control of claim 16, wherein the doubly-fed induction machine is employed as a generator, further comprising:(a) a first output that is adapted to operatively couple to a first switch that is disposed between the second polyphase stator winding and the AC line and is initially open so that the second polyphase stator winding is initially not coupled to the AC line by the switch;(b) a second output adapted to operatively control a second switch that is disposed between the second polyphase stator winding and a load and is initially open so that the second polyphase stator winding is initially not coupled to the load by the second switch; and(c) wherein the machine instructions further cause the processor to:(i) enable selective operation of the generator in one of a co-generation mode and a standalone mode, with the first switch and the second switch open, so that when operation in the co-generation mode is selected, the control:(1) prior to closing the first switch and in response to said one of the voltages that is being monitored, automatically regulates one of a polyphase voltage and a polyphase current applied to the first polyphase stator winding by the electronic power converter so as to cause the voltage across the first switch to approach a substantially zero value;(2) automatically closes the first switch when the voltage across the first switch while open is substantially zero; and(3) controls a current supplied to the AC line by the machine, by controlling the polyphase current supplied to the first polyphase stator winding by the electronic power converter; and(ii) when operation in the standalone mode is selected to energize the AC load, the control:(1) controls an output of the second polyphase stator winding with the electronic power converter, to attain a desired output; and(2) then closes the second switch to supply power to the load from the doubly-fed induction generator. 29. A method for generating variable speed constant frequency power with a doubly-fed induction generator that is driven by an engine, said generator having a polyphase first stator winding and a second stator winding that are substantially electrically and magnetically independent, and a brushless induction rotor assembly that magnetically couples the first and second stator windings in a reverse phase sequence, the method comprising the steps of:(a) coupling the polyphase first stator winding to a first set of AC power connections of an electronic power converter configured to operate as a variable voltage, variable frequency inverter, and coupling the second stator winding to a second set of AC power connections of the electronic power converter, said second stator winding also being selectively coupled to the load;(b) monitoring at least one phase of the second stator winding to produce signals indicative of one of:(i) a voltage and a frequency of said at least one phase; and(ii) a voltage and an electrical position of said at least one phase;(c) regulating a frequency of a voltage applied by the electronic power converter to the first stator winding so that the frequency of said at least one phase on the second stator winding is substantially constant;(d) regulating a voltage applied to the first stator winding by the electronic power converter so that the voltage on the second stator winding is substantially constant;(e) monitoring a current in at least one phase of one of the first stator winding and the second stator winding of said generator; and(f) controlling a speed of the engine in response to the current that is monitored, the engine thereby driving said generator at a speed sufficient to meet the load coupled to the second stator winding of said generator. 30. The method of claim 29, wherein the second set of AC power connections of the electronic power converter is connected to a rectifier bridge, and wherein a maximum speed of the engine is limited to that at which the frequency on the first stator winding is substantially equal to zero. 31. The method of claim 29, wherein the second set of AC power connections of the electronic power converter is connected to an inverter bridge that is synchronized with the frequency of the second stator winding and a current provided by the second set of The apparatus of claim power connections is regulated to maintain a DC bus voltage of the inverter bridge at a preset voltage above a peak second stator winding voltage, thereby enabling power to flow bidirectionally to and from the second stator winding. 32. The method of claim 29, further comprising the step of supplying electrical power from a secondary power source to energize the electronic power converter, until the second stator winding can supply the electrical power required to energize the electronic power converter.