Conventional Synchronous Machine Research Articles

Circuits and Systems Issues in Power Electronics Penetrated Power Grid

The penetration of power electronics into power generation and distribution systems has deepened in recent years, as prompted by the increasing use of renewable sources, the quest for higher performance in the control of power conversion, as well as the increasing influence of economic plans that necessitate power trading among different regions or clusters of power distribution. As a result of the increased use of power electronics for controlling power flows in power systems, interactions of power electronics systems and conventional synchronous machines’ dynamics would inevitably cause stability and robustness concerns, which can be readily understood by the coupling effects among interacting dynamical systems of varying stability margins (or transient performances). In this article, we present the various problems of power electronics penetration into power grids and the implications on the stability and robustness of power networks. We specifically attempt to bring together two distinct perspectives, namely, bottom-up (local) and top-down (global) perspectives, and examine the current progress and future direction of research in power systems amidst the extensive deployment of power electronics.

Design of a Novel Low-Cost Consequent-Pole Permanent Magnet Synchronous Machine

This article proposes a novel low-cost consequent-pole permanent magnet (CPM) synchronous machine structure, considering the reluctance torque utilization. First, a novel CPM machine with doubled salient ferromagnetic iron poles (ICP-PMSM) is proposed, featuring an N pole - iron - S pole - iron sequence to maximize the reluctance torque utilization and reduce cost. Flux barriers are integrated into the rotor structure to maintain the same magnetic rotor pole number as the conventional CPM synchronous machine (CP-PMSM). Second, for a low torque ripple, soft ferrite is used to replace part of the iron pole in the ICP-PMSM (ISCP-PMSM) to improve the air-gap flux density distribution. Furthermore, the CP-PMSM, ICP-SPMSM, and ISCP-PMSM rotors are optimized for a fair comparison. The electromagnetic performances of all the optimized machines are compared with those of a conventional surface permanent magnet synchronous machine (SPMSM). It is demonstrated that the ISCP-PMSM can obtain an almost equivalent torque and torque ripple, but with reduced PM (NdFeB) usage and cost when compared to the SPMSM.

Dual-Mode Wound Rotor Synchronous Machine for Variable Speed Applications

This paper presents a novel dual-mode wound rotor synchronous machine (DWRSM) for variable speed applications. The proposed machine combines the advantages of both the conventional wound rotor synchronous machine (CWRSM) and the brushless wound rotor synchronous machine (BWRSM). Unlike the existing BWRSM, through the dual-mode operation of the proposed machine, constant torque is achieved in the constant torque region by operating the machine in mode-I, i.e., as a CWRSM, and constant power is achieved in the field weakening region by operating the machine in mode-II, i.e., as a BWRSM. The mode change is performed through an additional thyristor drive circuit. The airgap magnetomotive force (MMF) in both modes is derived analytically. To verify this principle, finite element analysis (FEA) and an experiment on a 1- horsepower prototype machine was performed, and key influential factors were verified. The transients in the stator currents and torque during the mode change was analyzed. The test results validated the correctness of the theory and the FEA results.

Effect and Inhibition Method of Armature-Reaction Field on Superconducting Coil in Field-Modulation Superconducting Electrical Machine

This paper studies the special effects of the armature reaction field (ARF) on the SC coils in the field-modulation superconducting (SC) machines (FMSCMs). Through comparing with the conventional SC synchronous machines (SCSMs) with similar structure to the electrically-excited synchronous machine (EESM), some special characteristics of the ARF effect of the FMSCMs are found, namely, the ARF will generate abundant moving harmonics with high amplitudes in the airgap, including the fundamental harmonic, all of which are alternating external magnetic field relative to the SC coils. These alternating harmonics will increase the AC loss, and induce high voltages in the SC coils. In order to weaken the ARF effect, some inhibition methods are proposed from the perspective of electrical machine design. Finally, the proposed combined method of simultaneously adding damper-coils and copper shield layer on the double-stator FMSCM (DS-FMSCM) exhibits an excellent inhibition effect, making the harmonic level of the DS-FMSCM match with that of the SCSM, meanwhile, reducing the induced voltages in the SC coils from several hundred volts to several volts.

Analysis of virtual synchronous generator control and its response based on transfer functions

Virtual Synchronous Generator (VSG) control has been proposed as a means to control power electronics converter interfaced generation and storage which retains the dynamics of the conventional synchronous machine. This study provides a comprehensive, transfer function based, analysis of VGS control, which can be used as the basis for the design of VSG transient and steady-state performance. Based on a hardware validated, large signal model, a small signal model and associated transfer functions which describe the changes in real and reactive powers in response to changes in references and grid frequency disturbances. The derived transfer functions are used to obtain insight into the correct design of VSG controllers. The small signal models, transfer functions and associated analysis are validated by comparison with measured results on a scaled hardware system.

Topology Analysis, Design, and Comparison of High Temperature Superconducting Double Stator Machine With Stationary Seal

This paper proposes a high temperature superconducting (HTS) double stator machine (HTS-DSM), based on the magnetic field modulation principle. In the proposed HTS-DSM, the HTS field winding and the copper armature winding are separately located on the two stators, so that it overcomes the drawbacks caused by the coupling device for cryogenic transfer, the torque tube, the carbon brushes, and slip rings in the conventional HTS synchronous machines with the rotating field winding, bringing the merits of high reliability and low maintenance cost. Moreover, a method of amounting a ferromagnetic ring outside the HTS field winding is also proposed to reduce the negative effects of the armature reaction field on the HTS field winding, since the alternating current (AC) losses induced by the armature reaction field easily cause the quench of the HTS field winding. Totally four different topologies are proposed, and the operation principle of the HTS-DSMs is analyzed based on the magnetic field modulation principle. Then the design and optimization of the HTS-DSM is discussed in detail to present the main design parameters of the four topologies. Finally, the performance of the four different topologies are compared by the finite element analysis, the results reveal that the HTS-DSM with modular dewar and iron-teeth inner stator exhibits the merits of higher power density.

Grid-Supporting Inverters With Improved Dynamics

A new inverter control approach, called enhanced virtual synchronous machine (eVSM), is proposed based on the VSM concept. Unlike existing VSM approaches, the eVSM does not emulate the rotating inertia based on an assumption of the unlimited energy storage, but it deploys the physically existing inertia of the dc-link element. The eVSM adopts an innovative way of enlarging the inertia utilization range, which obviates the need for having a large dc-link element or a dedicated battery storage system, while still providing the same inertia response of an equivalent synchronous machine. Theoretical developments and numerical results presented in this paper confirm that the proposed eVSM can present a stabilizing support to the grid similar to a synchronous machine despite the small size of its dc-link element. Moreover, its transient responses can be improved beyond those of conventional synchronous machines thanks to the possibility of more flexibly adjusting damping and governor functions.

Comparison of different synchronous machines with stator‐side permanent magnets for industrial drive application

Three different synchronous machines with the permanent magnets in the stator (doubly salient permanent magnet, flux reversal permanent magnet, and flux switching permanent magnet machine) are compared for use as an industrial drive for 45 kW, 400 V Y, and 1000 …. 3000 min −1 . For comparison, finite element method simulations are carried out to investigate the torque density of the machines, and the results are explained based on the magnetic co-energy. The simulations show that the flux switching machine generates the highest torque density of the three machines. Therefore, a prototype flux switching machine is built, tested, and compared with a conventional permanent magnet synchronous machine (PMSM) with magnets on the rotor surface, the same size (stator outer diameter d so = 314 mm, axial length l Fe = 180 mm) and rating. The measurements indicate that the conventional PMSM and the flux switching machine have roughly equivalent electrical behaviour.

Linear consequent pole Halbach array flux reversal machine

This paper presents a linear variable reluctance permanent magnet (LVRPM) machine where the armature winding and inset Halbach array permanent magnets (PMs) are mounted on E-core stators. The Halbach array consists of a vertically magnetised PM pole and a salient ferromagnetic iron pole (split tooth) sandwiched between two horizontal PMs. The translator consists solely of laminations with salient iron poles. As a variable reluctance machine, it exhibits inherent magnetic gearing and a higher force and power density than the conventional synchronous PM machines. Finite element analysis (FEA) has been used to investigate the effect of machine parameters. The logical development of the LVRPM from the more conventional Vernier Hybrid machine is presented, including a near 50% reduction in magnetic flux leakage and a higher flux per unit magnet mass.

Analysis of a New Dual-Stator Vernier Machine With Hybrid Magnet Flux-Reversal Arrangement

This paper proposes a new hybrid magnet (HM) dual-stator vernier machine (DSVM) with flux-reversal (FR) magnet arrangement, in which NdFeB and ferrite magnets are reversely mounted on tooth tips of outer and inner stators, respectively. The hybrid dual excitation topology enhances the magnetic fields of inner and outer air-gaps, which are modulated by the rotor composed of iron poles. The proposed topology, operating principle, and design consideration are described. The merits of the proposed HM-FRDSVM are verified when compared to the same FRDSVMs with dual NdFeB magnet excitation and with dual ferrite magnet excitation and the conventional dual stator synchronous permanent magnet machine. The two-dimensional finite element analysis results show that the proposed machine has high torque cost performance with low torque ripple and low cogging torque that are desirable for large telescope drive application.

Relationship Between Homopolar Inductor Machine and Wound-Field Synchronous Machine

The homopolar inductor machine (HIM) has attracted recent interest in the field of flywheel energy storage system due to its merits of robust rotor and low idling losses. In some situations, the analytical methods of a conventional wound-field synchronous machine (WSM) can be used to analyze the HIM, but the clear explanation about why these can be done and the relationship between HIM and WSM were not given in the literature. To address these issues, this paper studies the HIM based on the basic theoretical model and equations. First, the structure and magnetic circuit characteristics of HIM are introduced. Second, the mathematical model of HIM is derived and then decomposed, which indicates that the HIM can be seen as a WSM with large end leakage inductance when rotor tooth width $ {\theta _t} \leq \pi /p$ , or a combination of WSM and synchronous reluctance machine (SynRM) when ${\theta _t} > \pi /p$ . Third, the performance indexes of HIM and corresponding equivalent machines, including air gap flux density, back electromotive force, and inductance parameters, are analyzed and fully compared. Finally, an HIM is prototyped and tested on an experimental platform. The simulation and experiment results show that it is reasonable to regard the HIM as a WSM or a combination of WSM and SynRM. The conclusion gives a transparent explanation about the relationship between HIM and WSM, which helps to simplify the analysis of the HIM.

A Novel Method of Frequency Regulation in Microgrid

Owing to generation and demand mismatch, the frequency deviation and the rate of change of frequency (RoCoF) may become drastic at times in an islanded microgrid. This is due to increased penetration of noninertial renewable energy sources that brings down the system's resilience to any kind of disturbance. Therefore, efficient control algorithms are required to mimic the inertial behavior of a conventional synchronous machine to arrest/limit any sudden change. This work focuses on frequency regulation of microgrid during transient conditions by means of fast-responding external energy reserve. The characteristics of a weak grid has been studied and simulated through modeling a virtual synchronous machine. An inverter model is also developed to integrate the energy storage system (ESS) to the grid and a double second-order generalized integrator phase locked loop (DSOGI-PLL) is implemented that is capable of synchronizing the system under distorted and unbalanced situation. A new technique to estimate the frequency of the microgrid is reported. A simple proportional controller-based approach for different level of pulsed power injection (using ultracapacitors and batteries) is proposed and simulated using MATLAB. Experimental demonstration is made using batteries only but with two different current-limits. The controller is implemented using dSPACE1103.

ELECTRIC GENERATOR IN THE RECUPERATION SYSTEM OF THE ENERGY FROM MECHANICAL OSCILLATIONS IN VEHICLES

The paper deals with the system of mechanical energy recuperation of vehicles in the useful electric energy accumulated in the rechargeable battery. This system creates an additional power supply on board of the vehicle and, based on the principle of energy conservation, increases the efficiency of the use of the fuel of the primary engine. One of the main elements of such system is an electric generator, which transforms the mechanical energy of the oscillations of the vehicle's chassis into electric energy. The problem of choosing and optimizing the design and parameters of the generator is considered in the paper. Given the peculiarities of the functioning of the vehicle, the most appropriate type of generator in such system is a synchronous generator with permanent magnet, which has significant structural differences from conventional synchronous machines with permanent magnets. The criterion for optimizing the generator is the largest value of the effective value of the EMF, which is induced in the stator winding. On the basis of simulation results, based on the field mathematical model, a set of values of generalized coefficients that characterize the optimal generator geometry is obtained.

A Variable Speed Pumped Storage System Based on Droop-Fed Vector Control Strategy for Grid Frequency and AC-Bus Voltage Stability

Harnessing wind energy is the most rapidly growing amongst renewable energy sources. However, because of its intermittency in nature, wind power results in unfavorable influences on power system control, operation and stability. The voltage sag and flicker and grid frequency fluctuation are significant in this regard. To minimize the effect of wind power fluctuations and other contingencies on the grid frequency and AC-bus voltage, this paper presents a droop-fed vector control strategy based variable speed pumped storage (VSPS) system comprising the doubly fed induction machine. Modelling of the system is undertaken based on a phasor model technique. The case study is made by considering the droop-controlled VSPS plant in a grid containing conventional synchronous machines for hydropower and thermal power plants and an induction machine wind farm. The performance is validated and analyzed using a MATLAB/Simulink platform. The proposed droop-fed control model is compared with the conventional control strategy (without being droop-fed) and tested to wind power fluctuations, start-up transients, load variations and three-phase fault. The results show that the droop-fed vector control strategy of the VSPS plant achieves better dynamic and steady state controlling responses for grid frequency and AC-bus voltage in the power system than the conventional vector control scheme during wind power fluctuations and contingencies.

Magnetic Gearing as a Functional Principle in Electric Drives

The partitioned stator flux reversal machine (PS-FRPM) is a novel stator PM machine topology, which exhibits a higher torque capability than its single stator counterpart and the conventional permanent magnet synchronous machine (PMSM). The PS-FRPM consists of two stators, one which carries the armature winding, and one which is equipped with surface mounted permanent magnets. The rotor is sandwiched between the two stators. The separation of the stator allows a better utilization of the machine volume which results in a higher torque density. Furthermore, because the magnets are placed on a stationary component, they can be cooled effectively. Consequently, critical rare-earth materials can be saved.The structure of the PS-FRPM is very similar to that of magnetic gears. In this paper the torque production of a PS-FRPM is described by means of the magnetic gearing effect. First the magnetic gearing effect is introduced and then the corresponding analytics is transferred to the PS-FRPM. Based on Maxwell's stress tensor, the torque contributions of the individual space harmonics are determined. In contrast to conventional machines, the torque in PS-FRPM is produced by several space harmonics in both air gaps.

Rotor Position Sensorless Control of Wound-Field Flux-Switching Machine Based on High Frequency Square-Wave Voltage Injection

This paper compares three shaft-sensorless control schemes for wound-field flux-switching machines based on a high frequency (HF) square-wave voltage injection technique. An HF model for the machine, with inclusion of the field winding, is first presented. Because the machine had armature and field windings, HF voltage is injected into and processed in the armature winding as with conventional permanent magnet synchronous machines (PMSMs) or injected into one winding and processed in the induced current signal in the other winding. Both the analytical and experimental results reveal that the scheme with $d$ -axis voltage injection and a $q$ -axis induced current process is generally similar to that used for PMSMs. Polarity identification is required to prevent phase errors in the estimated position. The schemes with separate windings for voltage injection and current processing demonstrate superior performance compared with the scheme without, and both schemes do not require polarity identification. Moreover, voltage injection at the field winding has an additional advantage for high-speed operations.

Towards the new energy storage system for conventional cars

Lead-acid batteries are widely used in conventional cars. This electric energy storage system (ESS) has to be capable to store enough energy for cranking the conventional car after the weeks without additional charging. After the start of internal combustion engine (ICE) of conventional car synchronous machine usually called alternator start to generate electrical energy. Electric current supplied in this way should be rectified and stored in lead-acid battery for the next start-up. In this article a model of whole process was developed and simulated. Particularly, a supercapacitors were compared with lead-acid batteries and other battery types in sense of mass, reliability and other parameters. Results were confirmed by measurement on conventional car. Furthermore, possibility of replacement of lead-acid batteries with supercapacitors was analyzed.

Performance Comparison of Conventional Synchronous Reluctance Machines and PM-Assisted Types with Combined Star–Delta Winding

This paper compares four prototype Synchronous Reluctance Motors (SynRMs) having an identical geometry of iron lamination stacks in the stator and rotor. Two different stator winding layouts are employed: a conventional three-phase star connection and a combined star–delta winding. In addition, two rotors are considered: a conventional rotor without magnets and a rotor with ferrite magnets. The performance of the four SynRMs is evaluated using a two-dimensional (2D) Finite Element Model (FEM). For the same copper volume and current, the combined star–delta-connected stator with Permanent Magnets (PMs) in the rotor corresponds to an approximately 22% increase in the output torque at rated current and speed compared to the conventional machine. This improvement is mainly thanks to adding ferrite PMs in the rotor as well as to the improved winding factor of the combined star–delta winding. The torque gain increases up to 150% for low current. Moreover, the rated efficiency is 93.60% compared to 92.10% for the conventional machine. On the other hand, the impact on the power factor and losses of SynRM when using the star–delta windings instead of the star windings is merely negligible. The theoretical results are experimentally validated using four identical prototype machines with identical lamination stacks but different rotors and winding layouts.

General Airgap Field Modulation Theory for Electrical Machines

This paper proposes a general field modulation theory for electrical machines by introducing magnetomotive force modulation operator to characterize the influence of short-circuited coil, variable reluctance, and flux guide on the primitive magnetizing magnetomotive force distribution established by field winding function multiplied by field current along the airgap peripheral. Magnetically anisotropic stator and rotor behave like modulators to produce a spectrum of field harmonics and the armature winding plays the role of a spatial filter to extract effective field harmonics to contribute the corresponding flux linkage and induce the electromotive force. The developed field modulation theory not only unifies the principle analysis of a large variety of electrical machines, including conventional dc machine, induction machine, and synchronous machine which are just special cases of the general field modulated machines, thus eliminating the problem of the machine theory fragmentation, but also provides a powerful guidance for inventing new machine topologies.

Research on system control and energy management strategy of flux-modulated compound-structure permanent magnet synchronous machine

The flux-modulated compound-structure permanent magnet synchronous machine (CS-PMSM), composed of a brushless double rotor machine (DRM) and a conventional permanent magnet synchronous machine (PMSM), is a power split device for plug-in hybrid electric vehicles. In this paper, its operating principle and mathematical model are introduced. A modified current controller with decoupled state feedback is proposed and verified. The system control strategy is simulated in Matlab, and the feasibility of the control system is proven. To improve fuel economy, an energy management strategy based on fuzzy logic controller is proposed and evaluated by the Urban Dynamometer Driving Schedule (UDDS) drive cycle. The results show that the total energy consumption is similar to that of Prius 2012.