Phase Transposition Research Articles

Vector Control of a Five-Phase Series-Connected Two-Motor Drive Using Synchronous Current Controllers

A novel concept for multi-motor drive applications has been developed recently, which enables dynamically decoupled control of all the machines in the group, although a single voltage source inverter is used as the supply. The concept requires utilization of multi-phase machines, whose stator windings have to be connected in series with an appropriate phase transposition, and it has been developed under the assumption that the inverter currents are controlled in the stationary reference frame. This article addresses the possibility of using synchronous current controllers within such a multi-motor drive system in order to realize fully decoupled dynamic control of all machines. The considerations of the article, although restricted to the series-connected two-motor five-phase drive system, can be extended to any other number of phases. It is shown that, in contrast to the situation that arises when current control is performed in the stationary reference frame, current control in the rotating reference frame requires appropriate modifications of the basic vector control scheme. The need for these modifications is explained and a method of realizing completely independent vector control of the two machines is proposed. The method is developed using rigorous mathematical modeling for the complete two-motor drive system. It is shown that completely decoupled dynamic control of the two machines results only if the calculation of the decoupling voltages during creation of machines' stator d-q axis voltage references is modified. Verification of the novel control scheme is provided by simulation.

Operating Principles of a Novel Multiphase Multimotor Vector-Controlled Drive

Independent flux and torque control of an ac machine can be achieved by means of vector control, utilizing only two stator d-q current components. Consequently, in ac machines with a phase number greater than three, there exist additional degrees of freedom. Although they can be used to enhance the torque production of a multiphase machine through injection of higher stator current harmonics, an entirely different purpose is possible as well. The additional degrees of freedom can be utilized to control independently other machines within a multimotor drive system. In order to do so, it is necessary to connect stator windings of all the multiphase machines in series, with an appropriate phase transposition, apply a vector control algorithm to each machine separately, and supply the stator windings of the multi-machine system from a single current controlled voltage source inverter (VSI). Inverter current control is performed in the stationary reference frame, using inverter phase currents. The foundations of the concept are set forth in the paper, for an arbitrary odd n-phase case, using the general theory of electrical machines. Further analysis is performed for all the theoretically possible odd phase numbers and it is shown that the number of machines connectable in series depends on the properties of the phase number. Connection diagrams are illustrated next for some selected phase numbers and vector control, including the inverter reference current generation, is detailed for the multimotor drive system. The main advantages and drawbacks of the concept are discussed and verification is provided by simulation of a nine-phase four-motor drive system.

Even-phase multi-motor vector controlled drive with single inverter supply and series connection of stator windings

Vector control principles enable independent flux and torque control of an AC machine by means of only two stator d-q axis current components. This means that in AC machines with a phase number greater than three there exist additional degrees of freedom, which are nowadays used to enhance the overall torque production of a multi-phase machine through injection of higher stator current harmonics. However, these additional degrees of freedom can be used to control other machines independently within a multi-motor drive system. To do so, it is necessary to connect in series stator windings of all the multi-phase machines, with an appropriate phase transposition. A vector control algorithm is then applied to each machine separately, total inverter phase current references are created by summation of individual machine phase current references, and supply to the stator windings of the multi-machine set is provided from a single current controlled voltage source inverter (VSI). The concept is introduced in the paper using the general theory of electrical machines, and all the possible situations that may arise for an even number of phases are examined. Although an induction motor drive is considered throughout, the concept is equally applicable to all AC machines with sinusoidal stator and rotor flux distribution. Its main advantage is the potential for saving in the number of inverter legs, compared to an equivalent 3-phase motor drive system. The saving depends on the number of phases and, for an even phase number, comes into existence when the number of phases is 8. Various even phase numbers are considered in detail and appropriate connection diagrams are given. Verification of the proposed multi-phase multi-motor drive is provided by simulation of a 10-phase 4-motor system.

Error of the Method of Determination of the Place of Damage of Overhead Lines Due to Ignored Phase Differences in Its Parameters

The effect of neglecting the influence of the phase asymmetry of parameters of overhead lines (OL) of different voltage classes on the accuracy of determination of the place of damage is discussed. The effect of phase transposition on the error of determination of the place of damage of a transmission line is evaluated by the methods of one-sided and two-sided measurement of the parameters of emergency operation. A method and software is suggested for substantial reduction of the error of the method of determination of the place of damage of overhead lines.

Fault analysis and component schemes for polyphase power systems

The application of component schemes for the analysis of fault currents in polyphase power systems is discussed. In particular, real transformations to components are derived, which are useful for transient analysis. Several possibilities are considered that are generalizations of the Clarke component scheme used for 3-phase power systems. It is shown that some schemes are valid only for polyphase power systems with complete phase transposition. The application of these real components to several types of shortcircuits is considered. Physical interpretation of the symmetrical and real components is made.