Six-phase Machine Research Articles

Series connected quasi-six-phase two-motor drives with independent control

Recent research has shown that it is possible to connect in series stator windings of multi-phase machines and control all the machines in the group independently using vector control principles, although the complete multi-drive system is supplied from a single multi-phase voltage source inverter (VSI). The concept has been investigated so far only for symmetrical n-phase machines (i.e., machines with spatial displacement between any two consecutive phases equal to 2 π/ n). This paper considers all possible configurations for the asymmetrical six-phase machines, with two three-phase stator windings displaced by 30°. Two possible two-motor configurations are presented. The first one utilises two quasi-six-phase machines while the second one connects in series a quasi-six-phase machine and a two-phase machine. Inverter current control schemes in both the stationary reference frame and the rotating reference frame are considered. Verification of the proposed multi-phase multi-machine drive is provided by simulation and the results are given in the paper.

Analysis of multiphase induction machines with winding faults

The paper shows how the techniques of generalized harmonic analysis may be used to simulate the steady-state behavior of a multiphase cage induction motor with any form of open-circuit or short-circuit fault in the stator winding. The analytical model is verified using a four-pole machine with a 48-slot stator. Each coil of the stator winding of this machine is brought out to a patchboard that enables the stator to be configured for single-phase, two-phase, three-phase, four-phase, six-phase, or 12-phase excitation. Experimental results are compared with computer predictions for a six-phase machine with both open-circuit and short-circuit faults.

A Series-Connected Two-Motor Six-Phase Drive With Induction and Permanent Magnet Machines

A novel concept for multimotor drives, based on utilization of multiphase machines, has been proposed recently. Independent vector control of all the machines of the group can be achieved while using a single multiphase inverter supply, provided that the stator windings are connected in series in an appropriate manner. One specific case of such a drive system is a two-motor drive, comprising a symmetrical six-phase machine connected in series with a three-phase machine. The group is supplied from a six-phase current-controlled voltage source inverter (VSI). The available considerations related to this two-motor drive system, consisting of two induction motors, are currently of purely theoretical nature, with the proof-of-concept provided by simulation only. This paper analyzes series-connected two-motor six-phase drive, comprising a six-phase symmetrical induction machine and a three-phase permanent magnet synchronous machine (PMSM) and provides, for the first time, detailed experimental verification of the possibility of independent control of the two motors. The operating principles of the drive system are at first reviewed and a brief description of the experimental system is then given. The emphasis is placed on an extensive presentation of experimental results, collected from a laboratory setup. It is shown that a truly independent and decoupled vector control of the two machines results, although a single supply source is used. The two-motor drive system of the proposed structure is seen as a potentially viable industrial solution for applications requiring one high-power and one low-power machine.

Vector control schemes for series-connected six-phase two-motor drive systems

A novel concept for multidrive systems, based on utilisation of multiphase machines, has been introduced recently. It has been shown that, by connecting in series stator windings of the multiphase machines in an appropriate manner, it becomes possible to control all the machines in the group independently using vector control principles, although the whole drive system is supplied from one multiphase voltage source inverter (VSI). The concept has been investigated so far only for true n-phase machines (i.e. machines with spatial displacement between any two consecutive phases equal to 2π/n) and all the available considerations are restricted to the inverter current control in the stationary reference frame. Moreover, all the available proofs of the decoupled dynamic control within these multidrive systems are simulation based. One specific case is discussed in detail; a two-motor series-connected six-phase drive supplied from a six-phase VSI. The two-motor drive system, based on utilisation of a true six-phase machine is considered first and, in addition to inverter current control in the stationary reference frame, inverter current control in the rotating reference frame is also analysed. It is shown that this method of current control requires modifications of the decoupling voltage terms, compared to those valid for a one-motor drive, this being caused by series connection of the two machines. Next, two-motor drives based on utilisation of quasi six-phase machines (with two three-phase stator windings displaced by 30°) are discussed and appropriate connection diagrams are developed. Verification of these schemes is provided by simulation. Finally, an experimental rig, which utilises a true six-phase machine connected in series with a three-phase machine and inverter current control in the stationary reference frame, is described and experimental verification of the decoupled dynamics of the two machines is provided by extensive testing.

Noise generation mechanisms in claw pole alternators

Noise of claw pole alternators, generated electromagnetically and structurally radiated, has been the subject of an extensive research program. The goal has been to identify and reduce noise radiation mechanisms in claw pole (Lundell) alternators used in automotive applications. Two approaches have been followed. In the first, electromagnetic sources of noise have been investigated by lumped parameter and magnetically equivalent circuit modeling and simulation, and by related experimentation. This is the subject of separate papers. The second, concurrent study reported here has investigated machine and mount responses to an electromagnetically generated torque ripple. Modeling and experimentation has led to the conclusion that there exists a high correlation between electromagnetic sources, torque ripple, and radiated noise. Experimentation also has led to the conclusion that noise characteristics of a given machine are substantially altered by modification of the mounting configuration. The work reported here involves modeling, simulation, and experiment to isolate machine dynamic characteristics and mounting geometries which contribute to strong coupling between torque ripple and machine/mount dynamic response. A low-order model of the alternator which includes shaft flexibility, gyroscopic effects, shaft bearing asymmetry, mounting lug geometry, and mounting structure dynamics has been created. The model provides a rapid simulation of dynamic response in the form of a transfer function between torque ripple and mounting forces. Generic studies of a simplified mounting structure coupled to the machine model are presented here. Acoustic testing of several machine configurations on a production mount has been carried out to investigate 36th order noise in three phase machines and 72nd order noise in six-phase machines. Electromagnetic modeling and dynamic response simulations suggest that the six-phase machine is inherently quieter. This is supported by experimental results. A test fixture for the measurement of torque ripple has been developed. Experimentation shows that the relative amplitudes of torque ripple in three- and six-phase machines correlates with relative noise levels. In addition, in torque ripple measurements, machine mounting characteristics are substantially altered and a predictably large reduction in radiated noise is realized.

The Ocurrence of Faults in LCI Drive Systems and its Effects on the Power Supply Quality

Like other drives, the LCI produce current harmonics, which are injected both in the machine and in the supply network. The last ones contribute to the degradation of the power supply, which have to comply with standards, regarding to the quality of electrical power systems [2]. To minimize the production of harmonics in the LCI, the structure adopted uses an asymmetrical six-phase machine, and the connection to the supply network is made through a transformer with two secondary windings constituting a twelve-pulse LCI drive system (Fig. 1).

Current regulator instabilities on parallel voltage-source inverters

Parallel inverters are often used to meet system power requirements beyond the capacity of the largest single structure. They have also been used to reduce harmonics, reduce pulsewidth modulation (PWM) switching frequency and increase available output voltage or frequency. The type of parallel structure depends on the construction of the load motor; the most prevalent are dual three-phase machines, split-phase machines, six-phase machines, and a standard three-phase machine with interphase reactors. Operation of parallel structures presents areas for investigation encompassing analysis, simulation, control, and design. This paper reports on the commissioning of a 775 HP dual-winding three-phase motor with parallel inverters. A simple method of paralleling structures with carrier-based PWM current regulators to independently regulate each inverter's current is employed. Experimental results show a loss of current control that is similar to a random event. The instability between the parallel inverters and the common motor can result in large uncontrolled currents. Simulations established that the reduction in controller gain, as the regulator enters the PWM pulse-dropping or overmodulation region, results in a loss of current control. Experimental results show the loss of current control is the result of an interaction between the parallel inverters through the dual-wound three-phase motor. Modifications were made to the modulator and a two-phase discontinuous controller was employed; the gain characteristic of the two-phase modulator in the overmodulation region extends the dynamic range of the motor drive.

Determination of damper winding and rotor iron currents in convertor- and line-fed synchronous machines

The damper winding currents of a synchronous machine with a solid iron rotor are analyzed. Based on the self and mutual inductance modelling technique, the damper currents are described by a detailed damper model taking the damper cage and the rotor iron into account. The model's component elements are determined by the finite element method. Theoretical results are verified by measuring damper bar currents of a six-phase synchronous machine fed by two six-pulse converters. For a number of different operating modes the model is used to calculate the damper current distribution of a six-phase machine. >

Low Torque Pulsation and High Power Control of Parmanent Magnet Motor with Distorted Electromotive Force.

This paper describes low torque pulsation and high power control of parmanent magnet synchro-nous motor (PM motor) with distorted electromotive force (emf).The experimental model of PM motor is 40kW, 190r/min, salient-pole, six-phase machine. An individual single-phase transistor inverter is connected to each phase of PM motor as a power source. By adopting full pitch and concentrated winding in the armature of the motor, the rate of flux utilization and output torque per mass can be increased. This winding causes trapezoidal distortion in the phase voltage waveform at no load. For realization of high peformance control of PM motor, the current waveform should be determined so as to minimize torque pulsation and maximize the output torque of the motor under the rated current.This paper proposes the method to determine the optimum current waveform. The currents and emf's are expressed as N-dimensional vectors (N: the number of phase). Due to the characteristics of the paticular structure of the motor, the armature reaction is small enough to be neglected. In this case, the optimum current vector can be derived under two conditions; (1) the direction of the current vector always agrees with that of the emf vector, and (2) the scalar product of the two vectors is held constant. Supplying the optimum current vector provides no torque pulsation and the nearly maximum output torque under the rated current. This method also can derive the new optimum current corresponding to open-phase operation.Validity of the method is experimentally confirmed. The characteristics of the experimental model of PM motor is also described in this paper.

Design and Control Techniques for Extending High Frequency Operation of a CSI Induction Motor Drive

An investigation of the maximum speed capability of a current source inverter (CSI) drive in both a three-and a six-phase connection is presented. It is shown that a six-phase configuration has distinct advantages over a three-phase connection in high speed capability for the same peak motor spike voltages. In addition, with proper control of the firing pulses fed to the inverters supplying the six-phase machine, the speed range can be substantially extended beyond the maximum limit predicted using conventional control. Predicted analytical results are correlated with results obtained by a detailed hybrid computer simulation.

65. Precision films for electronic components: Anon., New Scientist, 13 (279), 22 March 1962, 674

Noise of claw pole alternators, generated electromagnetically and structurally radiated, has been the subject of an extensive research program. The goal has been to identify and reduce noise radiation mechanisms in claw pole (Lundell) alternators used in automotive applications. Two approaches have been followed. In the first, electromagnetic sources of noise have been investigated by lumped parameter and magnetically equivalent circuit modeling and simulation, and by related experimentation. This is the subject of separate papers. The second, concurrent study reported here has investigated machine and mount responses to an electromagnetically generated torque ripple. Modeling and experimentation has led to the conclusion that there exists a high correlation between electromagnetic sources, torque ripple, and radiated noise. Experimentation also has led to the conclusion that noise characteristics of a given machine are substantially altered by modification of the mounting configuration. The work reported here involves modeling, simulation, and experiment to isolate machine dynamic characteristics and mounting geometries which contribute to strong coupling between torque ripple and machine/mount dynamic response. A low-order model of the alternator which includes shaft flexibility, gyroscopic effects, shaft bearing asymmetry, mounting lug geometry, and mounting structure dynamics has been created. The model provides a rapid simulation of dynamic response in the form of a transfer function between torque ripple and mounting forces. Generic studies of a simplified mounting structure coupled to the machine model are presented here. Acoustic testing of several machine configurations on a production mount has been carried out to investigate 36th order noise in three phase machines and 72nd order noise in six-phase machines. Electromagnetic modeling and dynamic response simulations suggest that the six-phase machine is inherently quieter. This is supported by experimental results. A test fixture for the measurement of torque ripple has been developed. Experimentation shows that the relative amplitudes of torque ripple in three- and six-phase machines correlates with relative noise levels. In addition, in torque ripple measurements, machine mounting characteristics are substantially altered and a predictably large reduction in radiated noise is realized.

61. Stress and magnetic anisotropy in thin permalloy films: M. Prutton, Nature, Lond., 193 (4815), 10 Feb. 1962, 565–566

Noise of claw pole alternators, generated electromagnetically and structurally radiated, has been the subject of an extensive research program. The goal has been to identify and reduce noise radiation mechanisms in claw pole (Lundell) alternators used in automotive applications. Two approaches have been followed. In the first, electromagnetic sources of noise have been investigated by lumped parameter and magnetically equivalent circuit modeling and simulation, and by related experimentation. This is the subject of separate papers. The second, concurrent study reported here has investigated machine and mount responses to an electromagnetically generated torque ripple. Modeling and experimentation has led to the conclusion that there exists a high correlation between electromagnetic sources, torque ripple, and radiated noise. Experimentation also has led to the conclusion that noise characteristics of a given machine are substantially altered by modification of the mounting configuration. The work reported here involves modeling, simulation, and experiment to isolate machine dynamic characteristics and mounting geometries which contribute to strong coupling between torque ripple and machine/mount dynamic response. A low-order model of the alternator which includes shaft flexibility, gyroscopic effects, shaft bearing asymmetry, mounting lug geometry, and mounting structure dynamics has been created. The model provides a rapid simulation of dynamic response in the form of a transfer function between torque ripple and mounting forces. Generic studies of a simplified mounting structure coupled to the machine model are presented here. Acoustic testing of several machine configurations on a production mount has been carried out to investigate 36th order noise in three phase machines and 72nd order noise in six-phase machines. Electromagnetic modeling and dynamic response simulations suggest that the six-phase machine is inherently quieter. This is supported by experimental results. A test fixture for the measurement of torque ripple has been developed. Experimentation shows that the relative amplitudes of torque ripple in three- and six-phase machines correlates with relative noise levels. In addition, in torque ripple measurements, machine mounting characteristics are substantially altered and a predictably large reduction in radiated noise is realized.