Multiphase Voltage Source Inverters Research Articles

Parallel-Connected Multiphase Multidrive Systems With Single Inverter Supply

Since independent control of an AC machine requires only two currents, additional degrees of freedom that exist in multiphase (n>3) machines can be used for other purposes. One possibility is the series connection of the stator windings, in an appropriate manner, which enables independent control of a set of machines although a single multiphase voltage-source inverter (VSI) is used as the supply. The concept has been explored recently in a considerable depth. This paper examines an alternative to the series connection, parallel connection of a multitude of multiphase machines supplied from a single VSI. This eliminates a shortcoming of the series arrangement, the requirement to have open-end stator winding machines. The general principles of paralleling the multiphase machines to a single multiphase VSI are at first set forth, with the subsequent development concentrating on the two-motor five-phase drive system. Dynamic and steady-state models of the two-motor drive are developed, and the vector control scheme is explained. Theoretical findings are verified by extensive experimental investigation on a laboratory setup. It is shown that parallel-connected multiphase multimotor drives represent an advanced example of the well-known analogy between series and parallel connection in electrical engineering. The quality of dynamic performance is the same as with series-connected drive systems. However, parallel connection suffers from a number of serious shortcomings that will prevent its application in industry.

Generalised space vector PWM for sinusoidal output voltage generation with multiphase voltage source inverters

The paper presents a generalised approach towards the development of the space vector pulse width modulation (SVPWM) for sinusoidal output voltage generation with two-level multiphase voltage source inverters (VSIs), where the number of phases is an odd number. The generalisation can greatly speed up the implementation since the tedious analysis of 2n voltage space vectors of an n-phase inverter in the corresponding (n − 1)/2 2-D planes can be completely avoided. Required dwell times for active space vectors are correlated with trigonometric properties of multiphase systems, which account for the actual phase number. Feasibility of the developed approach has been verified experimentally using the five-phase and seven-phase SVPWM schemes as examples.

Analytical Determination of DC-Bus Utilization Limits in Multiphase VSI Supplied AC Drives

Two-level multiphase voltage source inverters (VSIs) are typically used as the supply for multiphase machines. Such machines are often with concentrated winding in which case, certain low-order stator current harmonics are injected to provide torque enhancement. Also, a multimotor drive system can be realized by connecting a number of multiphase machines in series, using phase transposition while supplying the whole system from a single multiphase VSI. In both situations, it is important to know the limits of the inverter operation in the linear modulation region. This paper develops a simple method that enables analytical determination of the boundaries of the linear modulation region for all multiphase inverters with a prime number of phases. The limits are independent of the actual pulse width modulation (PWM) method utilized, and are equally applicable to both carrier-based and space vector PWM techniques. Theoretical considerations are verified experimentally using the five-phase and seven-phase VSI rigs.

Multiphase Electric Machines for Variable-Speed Applications

Although the concept of variable-speed drives, based on utilization of multiphase machines, dates back to the late 1960s, it was not until the mid- to late 1990s that multiphase drives became serious contenders for various applications. These include electric ship propulsion, locomotive traction, electric and hybrid electric vehicles, ldquomore-electricrdquo aircraft, and high-power industrial applications. As a consequence, there has been a substantial increase in the interest for such drive systems worldwide, resulting in a huge volume of work published during the last ten years. An attempt is made in this paper to provide a brief review of the current state of the art in the area. After addressing the reasons for potential use of multiphase rather than three-phase drives and the available approaches to multiphase machine designs, various control schemes are surveyed. This is followed by a discussion of the multiphase voltage source inverter control. Various possibilities for the use of additional degrees of freedom that exist in multiphase machines are further elaborated. Finally, multiphase machine applications in electric energy generation are addressed.

Induction Machine/Syn-Rel Two-Motor Five-Phase Series-Connected Drive

Multimotor drives, based on utilization of multiphase machines, have been proposed recently. Independent vector control of all the machines of the group can be achieved while using a single multiphase voltage source inverter supply, provided that the stator windings are connected in series in an appropriate manner. The concept is applicable to any system phase number greater than or equal to five. Detailed theoretical and simulation studies have been reported for multiphase multimotor drive configurations of this type and it has been suggested that the concept is valid regardless of the type of ac machines. This paper examines operation of such a drive system when a five-phase induction machine is connected in series with a five-phase synchronous reluctance machine and provides detailed experimental verification of the possibility of independent control of the two-motor drive comprising five-phase motors of different types. The operating principles of the drive system are at first reviewed and a brief description of the experimental system is then given. An extensive presentation of experimental results, collected from a laboratory setup, is further provided. It is shown that fully independent and decoupled vector control of the two machines results, although a single supply source is used.

Multiphase induction motor drives – a technology status review

The area of multiphase variable-speed motor drives in general and multiphase induction motor drives in particular has experienced a substantial growth since the beginning of this century. Research has been conducted worldwide and numerous interesting developments have been reported in the literature. An attempt is made to provide a detailed overview of the current state-of-the-art in this area. The elaborated aspects include advantages of multiphase induction machines, modelling of multiphase induction machines, basic vector control and direct torque control schemes and PWM control of multiphase voltage source inverters. The authors also provide a detailed survey of the control strategies for five-phase and asymmetrical six-phase induction motor drives, as well as an overview of the approaches to the design of fault tolerant strategies for post-fault drive operation, and a discussion of multiphase multi-motor drives with single inverter supply. Experimental results, collected from various multiphase induction motor drive laboratory rigs, are also included to facilitate the understanding of the drive operation.

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.

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.