Multi-phase electric motor with third harmonic current injection

A method of controlling an electrical motor having a stator with a core, two three-phase windings wound on the core, the two three-phase windings separated spatially by 30 electrical degrees, each of the two three-phase windings having three terminals and a neutral terminal by which power may be applied to the three-phase windings, and a rotor within the stator, comprising the steps of:

• (a) applying current at a fundamental frequency and zero sequence current at a third harmonic of the fundamental frequency to the terminals of a first of the two three-phase windings;
• and
• (b) applying current at the same fundamental frequency and zero sequence current at the same third harmonic frequency to the terminals of a second of the two three-phase windings but shifted in time by 30° of the fundamental frequency current with respect to the current provided to the first of the three-phase windings.

A linear motor drive system comprising:

• (a) a linear induction motor having a stator with at least one core, two three-phase windings wound on the core, the two three-phase windings separated spatially by 30 electrical degrees, each of the two three-phase windings having three terminals and a neutral terminal by which power may be applied to the windings, and an induction machine linear rotor;
• and
• (b) a first power supply connected to the terminals of a first of the stator three-phase windings and a second power supply connected to the terminals of a second of the stator three-phase windings, the power supplies formed to provide current to the two three-phase windings with the same fundamental frequency and with an additional zero sequence component at the third harmonic of the fundamental frequency with one of the power supplies providing current to one of the three-phase windings that is shifted in time by 30° of the fundamental frequency current with respect to the current provided by the other power supply.

A method of controlling a linear induction motor having a stator with at least one core, two three-phase windings wound on the core, the two windings separated spatially by 30 electrical degrees, each of the two three-phase windings having three terminals and a neutral terminal by which power may be applied to the three-phase windings, and an induction machine linear rotor, comprising the steps of:

• (a) applying current at a fundamental frequency and a zero sequence current at a third harmonic of the fundamental frequency to the terminals of a first of the two three-phase windings;
• and
• (b) applying current at the same fundamental frequency and zero sequence current at the same third harmonic frequency to the terminals of a second of the two three-phase windings but shifted in time by 30° of the fundamental frequency current with respect to the current provided to the first of the three phase windings.

A motor drive system comprising:

• (a) an induction motor having a stator with a core, two three-phase stator windings wound on the core, the two three-phase windings separated spatially by 30 electrical degrees, each of the two three-phase windings having three terminals and a neutral terminal by which power may be applied to the three-phase windings, and an induction machine rotor within the stator;
• and
• (b) a first power supply connected to the terminals of a first of the stator three-phase windings and a second power supply connected to the terminals of a second of the stator three-phase windings, the power supplies formed to supply current to the two three-phase windings with the same fundamental frequency and with an additional zero sequence component at the third harmonic of the fundamental frequency, with one of the power supplies providing current to a one of the three-phase windings that is shifted in time by 30° of the fundamental frequency current with respect to the current provided by the other power supply.

A method of controlling an electrical motor having a stator with a core, two three-phase windings wound on the core, the two three-phase windings separated spatially by 30 electrical degrees, each of the two three-phase windings having three terminals and a neutral terminal by which power may be applied to the three-phase windings, and an induction machine rotor within the stator, comprising the steps of:

• (a) applying current at a fundamental frequency and zero sequence current at a third harmonic of the fundamental frequency to the terminals of a first of the two three-phase windings;
• and
• (b) applying current at the same fundamental frequency and zero sequence current at the same third harmonic frequency to the terminals of a second of the two three-phase windings but shifted in time by 30° of the fundamental frequency current with respect to the current provided to the first of the three-phase windings.

A motor drive system comprising:

• (a) an induction motor having a stator with a core, three three-phase stator windings wound on the core, a second and third of the three-phase windings separated spatially by 20 and 40 electrical degrees, respectively, from a first of the three-phase windings, each of the three three-phase windings having three terminals by which power may be applied to the three-phase windings, and an induction machine rotor within the stator;
• and
• (b) a first power supply connected to the terminals of a first of the stator three-phase windings, a second power supply connected to the terminals of a second of the stator three-phase windings, and a third power supply connected to the terminals of a third of the stator three-phase windings, the power supplies formed to supply current to the three three-phase windings with the same fundamental frequency and with an additional component at the third harmonic of the fundamental frequency, the second power supply providing current that is shifted in time by 20° of the fundamental frequency current and the third power supply providing current that is shifted in time by 40° of the fundamental frequency current with respect to the current provided by the first power supply.

A power supply system for an induction motor having two three-phase stator windings with three terminals and a neutral terminal by which power may be applied to the three-phase windings comprising:

• a first power supply connectable to the terminals of a first of the three-phase windings and a second power supply connectable to the terminals of a second of the three-phase windings, the power supplies formed to supply current with the same fundamental frequency and with an additional zero sequence component at the third harmonic of the fundamental frequency, with one of the power supplies providing current that is shifted in time by 30° of the fundamental frequency current with respect to the current provided by the other power supply, wherein the power supplies are inverters that receive DC power on DC bus lines, and a rectifier connected to rectify AC power to DC voltage supplied to the DC bus lines, a pair of smoothing capacitors connected together at a node and connected across the DC bus lines, wherein the neutral terminals of the three-phase windings are connectable to the node between the capacitors.