Secondary magnetic excitation generator-motor device

A secondary magnetic excitation generator-motor device comprising:

• a winding induction machine with a stator-side armature winding being connected to an AC system;
• a three-level NPC power converter to which a rotor-side excitation winding of the winding induction machine is connected;
• a first DC capacitor connected between a positive DC terminal and a neutral point of the three-level NPC power converter;
• a second DC capacitor connected between the neutral point and a negative DC terminal of the three-level NPC power converter;
• a DC voltage source to supply a DC voltage to the first DC capacitor and the second DC capacitor;
• an excitation current detector to detect an excitation winding current of the winding induction machine;
• and
• an excitation current command device to compute an excitation current command value with a slip frequency equal to a difference between a frequency of the AC system and a rotational frequency of the winding induction machine, and to output a first ignition pulse command such that a detected excitation current value from the excitation current detector corresponds with the excitation current command value,
• wherein the secondary magnetic excitation generator-motor device is configured to input the first ignition pulse command to a self-arc-extinguishing semiconductor element of the three-level NPC power converter,
• wherein the secondary magnetic excitation generator-motor device has a function of identifying a first phase, a second phase, or a third phase in descending order of a current absolute value from the excitation current detector,
• wherein the secondary magnetic excitation generator-motor device further comprises a pulse command device configured to:
• separate four series-connected self-arc-extinguishing semiconductor elements formed of a self-arc-extinguishing semiconductor element P1C between the first phase and a positive-side clamp diode, a self-arc-extinguishing semiconductor element P1 between the self-arc-extinguishing semiconductor element P1C and a positive electrode, a self-arc-extinguishing semiconductor element N1C between the first phase and a negative-side clamp diode, and a self-arc-extinguishing semiconductor element N1 between the self-arc-extinguishing semiconductor element N1C and a negative electrode into a first-phase P group formed of the self-arc-extinguishing semiconductor element P1 and the self-arc-extinguishing semiconductor element PIC, and a first-phase N group formed of the self-arc-extinguishing semiconductor element N1 and the self-arc-extinguishing semiconductor element N1C;
• determine a polarity of a detected current value for the first phase;
• fix an ignition pulse in either the first-phase P group or the first-phase N group to an on-side, while fixing an ignition pulse in the other group to an off-side in a direction in which the first and second DC capacitors are charged;
• separate four series-connected self-arc-extinguishing semiconductor elements formed of a self-arc-extinguishing semiconductor element P2C between the second phase and a positive-side clamp diode, a self-arc-extinguishing semiconductor element P2 between the self-arc-extinguishing semiconductor element P2C and a positive electrode, a self-arc-extinguishing semiconductor element N2C between the second phase and a negative-side clamp diode, and a self-arc-extinguishing semiconductor element N2 between the self-arc-extinguishing semiconductor element N2C and a negative electrode into a second-phase P group formed of the self-arc-extinguishing semiconductor element P2 and the self-arc-extinguishing semiconductor element P2C, and a second-phase N group formed of the self-arc-extinguishing semiconductor element N2 and the self-arc-extinguishing semiconductor element N2C;
• fix an ignition pulse in the second-phase P group to a same side as the first-phase N group, while fixing an ignition pulse in the second-phase N group to a same side as the first-phase P group;
• to separate four series-connected self-arc-extinguishing semiconductor elements formed of a self-arc-extinguishing semiconductor element P3C between the third phase and a positive-side clamp diode, a self-arc-extinguishing semiconductor element P3 between the self-arc-extinguishing semiconductor element P3C and a positive electrode, a self-arc-extinguishing semiconductor element N3C between the third phase and a negative-side clamp diode, and a self-arc-extinguishing semiconductor element N3 between the self-arc-extinguishing semiconductor element N3C and a negative electrode into a third-phase first group formed of the self-arc-extinguishing semiconductor element P3C and the self-arc-extinguishing semiconductor element N3C, and a third-phase second group formed of the self-arc-extinguishing semiconductor element P3 and the self-arc-extinguishing semiconductor element N3;
• fix an ignition pulse in the third-phase first group to on, while fixing an ignition pulse in the third-phase second group to off;
• output the ignition pulses as a second ignition pulse command, and
• wherein a pulse switch is provided to switch between the first ignition pulse command and the second ignition pulse command bidirectionally to be output to the three-level NPC power converter, so that on conditions including a condition that any of absolute values of detected current values from the excitation current detector exceeds a set overcurrent level 1, the pulse switch switches from a first ignition pulse command to a second ignition pulse command, and on conditions including a condition that detected current values for three phases from the excitation current detector are all equal to or smaller than a set overcurrent level 2, the pulse switch switches from the second ignition pulse command to the first ignition pulse command.