The main objective of this two-part state-of-the-art paper called “Recent Advances in the Design, Modeling, and Control of Multiphase Machines” is to present latest contributions in the multiphase machines' field. The first part of this paper focuses on the recent progress in the design, modeling, and control, whereas the drive is in healthy operation. This second part presents relevant contributions in two not analyzed fields. The first is in relation with the use of the additional degrees of freedom of multiphase machines and the exploitation of their fault-tolerant capabilities without adding extra hardware. The second one analyzes multiphase generation, particularly in grid-connected wind energy conversion systems and stand-alone applications. Recent progresses are shown and open challenges and future research directions are discussed.

Recent Advances in the Design, Modeling, and Control of Multiphase Machines—Part II

Some design and operation aspects of axial flux permanent magnet synchronous machines, wound with concentrated coils, are presented. Due to their high number of poles, compactness, and excellent waveform quality and efficiency, these machines show satisfactory operation at low speeds, both as direct drive generators and as motors. In this paper, after a general analysis of the model and design features of this kind of machine, the attention is focused on wind power generation: The main sizing equations are defined, and the most relevant figures of merit are examined by means of a suitable parametric analysis. Some experimental results obtained by testing a three-phase, 50-kW, and 70-rpm prototype are presented and discussed, validating the modeling theory and the design procedure.

Axial Flux PM Machines With Concentrated Armature Windings: Design Analysis and Test Validation of Wind Energy Generators

This paper discusses the operation of a multiphase system, which is aimed at both variable-speed drive and generating (e.g., wind energy) applications, using back-to-back converter structure with dual three-phase machine-side converters. In the studied topology, an asymmetrical six-phase induction machine is controlled using two three-phase two-level voltage source converters connected in series to form a cascaded dc link. The suggested configuration is analyzed, and a method for dc-link midpoint voltage balancing is developed. Voltage balancing is based on the use of additional degrees of freedom that exist in multiphase machines and represents entirely new utilization of these degrees. The validity of the topology and its control is verified by simulation and experimental results on a laboratory-scale prototype, thus proving that it is possible to achieve satisfactory dc-link voltage control under various operating scenarios.

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Operation of a Six-Phase Induction Machine Using Series-Connected Machine-Side Converters

The stator permanent magnet (PM) machines have simple and robust rotor structure as well as high torque density. The hybrid excitation topology can realize flux regulation and wide constant power operating capability of the stator PM machines when used in dc power systems. This paper compares and analyzes the electromagnetic performance of different hybrid excitation stator PM machines according to different combination modes of PMs, excitation winding, and iron flux bridge. Then, the control strategies for voltage regulation of dc power systems are discussed based on different critical control variables including the excitation current, the armature current, and the electromagnetic torque. Furthermore, an improved direct torque control (DTC) strategy is investigated to improve system performance. A parallel hybrid excitation flux-switching generator employing the improved DTC which shows excellent dynamic and steady-state performance has been achieved experimentally.

Hybrid Excitation Topologies and Control Strategies of Stator Permanent Magnet Machines for DC Power System

A partitioned stator hybrid excited machine is proposed, in which the permanent magnets and field windings are alternately placed on an inner stator separated from the outer stator having armature windings. This machine inherits the features of brushless machines and benefits from better space utilization. The operating principle and the effects of slot/pole combinations are investigated in detail. Further, based on 2-D finite-element analysis, the electromagnetic performances of the proposed machines, including back-electromotive force, cogging torque, flux regulation range, torque capability, power factor and torque–speed curve, are evaluated. The results reveal that the proposed machines can exhibit wide flux regulation range as well as good torque density. The prototype is manufactured and tested to validate the predictions.

Novel Consequent-Pole Hybrid Excited Machine With Separated Excitation Stator

We present a new topology of hybrid excitation synchronous machine (HESM) and describe operational principles and features of the new configuration. Using the radial/axial distribution of the magnetic field, we develop an equivalent magnetic circuit model. We obtain magnetic flux, flux density, and induced voltage with various electrical magnetomotive forces by calculating the nonlinear magnetic circuit equation. We studied the Influence on the radial magnetic field of the axial magnetic field by 3-D finite-element method. The results are in good agreement with calculation by our magnetic circuit model. Our findings indicate that the air-gap flux density of a flux-concentrating HESM is high and the magnetic field in the air gap can be successfully regulated. Experimental results of 3 kVA prototype machine verify the feasibility of the structure and the correctness of our analysis.

Principle of Operation and Feature Investigation of a New Topology of Hybrid Excitation Synchronous Machine

Six-phase double-star armature windings of a synchronous generator are essentially equivalent to 12-phase symmetrical windings displaced in turn by 30deg. This paper proposes and implements a new permanent-magnet brushless dc (BLDC) generator using 12-phase half-wave rectifier. Characteristic of output voltage is analyzed according to the star graph of slot potential, and the design constraints of armature windings are provided. Simulation models of 12-phase synchronous generator with half-wave rectifier and double-star synchronous generator with bridge rectifier are established separately. Field-circuit-coupled analysis is accomplished, and conducted modes of rectified diodes and output characteristic are obtained. It is shown that the current stress of diodes in 12-phase rectification system is less than half of that in double-star rectification system, and the output voltage fluctuation between the two different rectification systems is similar. Experimental results on prototype machine, which agree well with the simulation analysis, also verify the feature of the proposed BLDC generator system.

Development of a New Permanent-Magnet BLDC Generator Using 12-Phase Half-Wave Rectifier

As for interior configuration of generator, six phase Y-Y armature windings is essentially equivalent to twelve-phase symmetrical windings displaced in turn by 30deg. Novel twelve- phase synchronous generator-rectifier system is developed in this paper. Characteristic of output voltage is analyzed in detail according to the star graph of slot potential, and then the design principle of armature windings in twelve-phase synchronous generator is provided. Utilizing the design of full-pitch-winding, the top-width angle of phase voltage waveform may greater than 120deg electric angle. It can be seen through theoretical analysis that the number of conductive rectifier diodes is not less than four. Based on a permanent magnet synchronous generator, field-circuit coupled models of twelve-phase rectifier system and six-phase Y-Y rectifier system are established separately in the Maxwell2D plus Simplorer soft environment, and the finite element analysis is accomplished. The analysis results validate the design principle of armature windings. Moreover, the number of rectifier diodes in twelve-phase synchronous generator-rectifier system is as same as that of six-phase Y-Y rectifier system, the current stress of rectifier diodes is reduced by half at least.

Zhou Bo

Papers

Principle of Operation and Feature Investigation of a New Topology of Hybrid Excitation Synchronous Machine

Development of a New Permanent-Magnet BLDC Generator Using 12-Phase Half-Wave Rectifier

Study on novel twelve-phase synchronous generator rectifier system