
Rong-Jie WangStellenbosch University | SUN · Department of Electrical & Electronic Engineering
Rong-Jie Wang
PhD (Eng)
About
142
Publications
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Introduction
Field of interest: special electrical machines, finite element method based design optimization, renewable energy systems, electrical traction, cooling design and analysis.
Additional affiliations
January 2010 - December 2013
January 2014 - September 2020
Education
January 1999 - March 2003
February 1996 - June 1998
Publications
Publications (142)
Axial Flux Permanent Magnet (AFPM) brushless machines are modern electrical machines with a lot of advantages over their conventional counterparts. They are being increasingly used in consumer electronics, public life, instrumentation and automation system, clinical engineering, industrial electromechanical drives, automobile manufacturing industry...
Energy storage is a crucial technology for facilitating the integration of renewable energy sources (RES), such as wind and solar energy, into the electrical grid. The challenge of maintaining a balance between incoming and outgoing grid power can be effectively addressed by integrating energy storage technologies with inherently intermittent RES....
Permanent magnet (PM) motors are increasingly used in high-power applications such as marine propulsion systems, where their exceptional torque density and efficiency are paramount. The configuration of PMs significantly affects the motor's performance and cost, making it a key design consideration. This study focuses on the design, optimization, a...
This paper studies the impact of permanent magnet eddy currents on three-phase short-circuit behavior in traction motors. A semi-analytical method is presented, allowing for an evaluation of the sub-transient short circuit behavior resulting from eddy currents. Furthermore, based on typical parameters of traction motors, a fast assessment of the re...
Since the advent of rare-earth permanent magnet (PM) materials, PM synchronous machines (PMSMs) have become popular in power generation, industrial drives, and e-mobility. However, rare-earth PMs in PMSMs are prone to temperature- and operation-related irreversible demagnetization. Additionally, faults can endanger components like inverters, batter...
The shipping industry is shifting towards efficient and environmentally friendly propulsion systems to reduce costs and ecological impact. Traditional diesel engines, predominant in maritime operations, face challenges of high operating costs and environmental pollution, prompting the exploration of alternatives. Electric propulsion emerges as a pr...
This paper proposes an AC copper loss calculation method for flat wire windings of pulse width modulation (PWM) driven permanent magnet (PM) synchronous motors. To quickly account for the effect of high frequency current harmonics on the magnetic field and losses, a semi-analytical eddy current loss calculation method is developed. This method comb...
The evolution of electric propulsion systems in the maritime sector has been influenced significantly by technological advancements in power electronics and machine design. Traditionally, these systems have employed surface-mounted permanent magnet synchronous motors (PMSMs) in podded configurations. However, the advent of permanent magnet Vernier...
For small-scale wind generators to operate efficiently in remote and residential areas, careful consideration must be given to the selection of the generator topology. The purpose of this study is to conduct an in-depth comparison of various design options available for wind generators. These designs include a permanent magnet vernier generator (PM...
The Permanent Magnet Vernier Motor (PMVM) is a novel type of permanent magnet motor that has attracted considerable attention in recent years due to its ability to
directly connect to the load. It exhibits remarkable efficiency across a wide range of speeds by employing the modulation effect, a technique that intentionally mismatches rotor and stat...
Permanent magnet synchronous machines (PMSMs) play a major role in large electric transportation such as electric ships. This is so because of its high efficiency and high torque density. However, for these large propulsion drive applications, high quality sensorless control is extremely important. Hence, in this paper the methods and performances...
This paper proposes a multivariable-sliding-mode extremum-seeking (MSES)-based adaptive PI method for sensorless speed control of high-power propulsion permanent magnet synchronous motor (PMSM) applications. Unlike the offline tuning PI controllers, the proposed controller incorporates adaptive tuning laws that dynamically adjust the control gains...
Permanent Magnet Vernier Motor (PMVM) is a new generation of permanent magnet (PM) motor that has attracted attention for direct drive applications, thanks to its
ability to generate high torque, achieved through flux modulation effects. Many comparisons have been made between permanent magnet synchronous motors (PMSMs) and PMVMs in terms of perfor...
In this paper, a study of sensorless control of a dual three-phase permanent magnet synchronous machine (DTP-PMSM) for ship-propulsion applications is presented. A
nonsingular terminal sliding mode observer is developed for fast and precise estimation of speed and position. The alpha-beta decomposition method is used to simplify the model of the DT...
In this study, two different design-options of the linear permanent magnet flux switching machine (LPM-FSM) are analyzed. The linear machine is used to move a hexagonal piston mass in dry gravity energy storage application for renewable energy integration on the grid. Design-option M1 consists of modular structure with the coils having end windings...
With the decrease in grid strength due to the increase in inverter-based renewable energy systems, this paper considers an alternative strong-grid-forming (SGF) systems, with specific focus on wind energy. For strong grid forming, battery
storage plays an inevitable role. In this paper, two systems are proposed and evaluated on a 5-MW power level,...
Since the advent of rare-earth permanent magnet (PM) materials, the PM synchronous machine (PMSM) has gained popularity in various applications, including power generation systems, industrial drives, and e-Mobility. However, the rare-earth PMs commonly used in PMSMs are inherently prone to both temperature and operation related irreversible demagne...
Despite the fact that conventional three-phase permanent magnet (PM) motors have dominated the market in recent years, multi-phase PM motors are progressively gaining popularity due to the safety and high-power requirements of certain applications. In this study, a 5-MW fractional-slot permanent magnet vernier motor (PMVM) for ship propulsion is de...
This paper proposes an enhanced fast terminal sliding-mode observer (FTSMO) for the wide-speed sensorless control of a vernier machine used in ship-propulsion system. The method enables speed and position estimation in the dq frame,
where, unlike the back-electromotive force (EMF) estimation based methods, the need for the phase lock loop (PLL) blo...
In recent years, the field of electrical machine technologies has experienced significant growth, primarily driven by the introduction of new materials, innovative machine topologies, and drive technologies, as well as expanding application areas, coupled with stricter energy efficiency regulations. This upsurge in the field has prompted researcher...
In this paper, the authors address the issue of the flux-modulated magnetic gear (FMMG), which offers many potential advantages over traditional mechanical gears for a wide range of applications. In the proposed FMMG model, two permanent magnet (PM) carriers are of different pole-pairs and rotate asynchronously, and their relative angular position...
The intermittent nature of renewable energy sources brings about fluctuations in both voltage and frequency on the power network. Energy storage systems have been utilised to mitigate these disturbances hence ensuring system flexibility and stability. Amongst others, a novel linear electric machine-based gravity energy storage system (LEM-GESS) has...
This paper presents an overview of various sensorless control methods, with a focus on dual three-phase permanent magnet synchronous machines (DTP-PMSM). Owing to the important role that DTP-PMSMs play in motion-control applications in industry, most academic researchers and industry activists seek to reduce costs and size while increasing the capa...
With more stringent IEC energy efficiency standards, electrical machine industry increasingly focuses on new motor technologies. Amongst others, the line-start permanent magnet synchronous machine (LSPMSM) is considered as an attractive alternative to induction machine, especially for low power and fixed-speed applications. However, the design of L...
This paper focuses on a consequent pole linear vernier hybrid machine for use in dry gravity energy storage systems. The consequent pole linear vernier hybrid machine acts as the main drive unit for raising and lowering a 50 ton piston that stores electrical energy as potential energy. Based on the magnetic gearing principles, this type of machine...
This paper investigates the prospect of permanent magnet vernier machine (PMVM) technology for wind power applications. Two types of PMVMs are defined based on the winding arrangements and resultant gear ratio ranges. A comprehensive design study of the selected PMVM topologies is conducted at 1 and 3 MW power levels. The optimized candidate design...
Brushless stator-mounted traction motors, which are new and emerging, have many potential applications in the electrified transport industry. Brushless stator-mounted machines (BSSMs), with the so-called flux modulation (FM) effects, use asynchronous field harmonics to realize energy conversion by altering the basic principle for conventional machi...
In this paper, two design optimisation methods are evaluated using gradient-based optimisation for electric vehicle traction applications. A driving cycle-based approach is used to evaluate specific operational points for the design optimisation procedure. To determine the operational points, an energy centre of gravity (ECG) approach is used. Both...
In this paper the design of a 130 kW linear electric machine for use in dry gravity storage system is presented. The linear electric machine makes use of a hybrid permanent magnet vernier machine with consequent poles. The linear machine is optimally
designed for a 100m high shaft for primary response application, raising and lowering a piston of 5...
Energy storage technologies have been gaining increasing attention as a way to help integrate variable and intermittent renewable energy sources into the grid. In this paper, a novel gravity energy storage system which features a linear electric machine-based hoisting mechanism is investigated. The storage system utilises the inherent ropeless oper...
Permanent magnet Vernier machines are well suited for direct-drive industrial applications such as ship propulsion drives, because of their ability to generate high torque at low speeds. In this paper, a flux-barrier tapered-U-shaped permanent magnet Vernier (FBU-PMV) machine topology is proposed. This topology is compared with the spoke-array perm...
This paper covers the design methodologies and optimisation techniques studied in the performance improvement of line-start permanent magnet synchronous motors (LSPMSM). LSPMSM performance improvement using design techniques are chiefly limited to either the transient or the steady-state performance improvement, and a focus on only the transient pe...
This paper presents an analytical method for modelling the no-load air gap flux density of a surface-mounted and a consequent-pole linear Vernier hybrid machine (LVHM). The approach is based on simple magneto-motive force (MMF) and permeance functions to account for the doubly-slotted air gap of the LVHM. These models are used to determine the flux...
Electric vehicles (EV) are increasingly used in both urban and industrial environments. Electric motors are the essential part of the EV power train systems. Different types of electric motor technologies have been developed for the purpose. Amongst others, permanent magnet synchronous motors (PMSM) are widely used for EV applications because of th...
An air-cooled double-rotor AFPM machine developed at the Electrical Machines Laboratory (EMLab) of Stellenbosch University in 2002, where: (a) rotor disc with surface-mounted PMs, (b) coreless stator with busbars, and (c) the assembled machine.
The picture shows the 15 kW PM Vernier wind generator developed at the Electrical Machines Laboratory (EMLab) of Stellenbosch University. The generator operates at 150 rpm and a rated torque of 1000 Nm.
This paper investigates the feasibility of using permanent magnet vernier machine technology for large wind power applications. Optimal permanent magnet vernier machine designs rated at 1MW and 3MW and with different gear-ratios are generated through the use of multi-objective finite element based design optimization. The designs are then evaluated...
In this paper a surface-mounted permanent magnet motor with a distributed overlapping winding is designed for a light electric vehicle. The motor specifications are derived
from the vehicle physics model where the operating points are determined. A theoretical understanding is developed of how to improve the motor’s speed range through changes in t...
Optimization of electrical machines is a challenging task that can be solved using either gradient based or non-gradient based methods. While gradient based methods are
theoretically much more efficient, their performance is often compromised in applications where finite element analyses are used for performance evaluation. In this paper, a common...
In this paper, the force ripple and cogging force minimisation of single-sided consequent-pole linear vernier hybrid machines is investigated through the use of the Taguchi method. The study focuses on obtaining robust designs that minimise the force ripple and cogging force through optimal tapering of the translator teeth, the soft ferromagnetic c...
In recent years, the permanent magnet Vernier machine (PMVM) has attracted much attention in the research community. Many studies have shown that PMVMs possess superior torque density and are suitable for high torque and low speed applications. Some of them compared PMVMs with the direct-drive permanent magnet synchronous machines (PMSM), but these...
In this paper, a robust design framework is proposed to mitigate torque ripple for line-start permanent magnet synchronous machines (LS-PMSM) by using the Taguchi method. The framework is intended for fine-tuning initial optimum designs to further improve the steady-state torque quality of LS-PMSMs. The proposed framework was successfully implement...
In this paper, a strategy for designing induction motors for traction applications is proposed. The proposed strategy builds on the conventional design of induction motors, but makes emphasis on the differentiating characteristics, which are the constant power speed ratio and overloading capability. A design procedure, which breaks up the motor des...
This paper discusses the design optimization and comparison of four permanent magnet machines with different rotor topologies for a 2kW traction application. The rotor topologies considered include the surface mount, spoke type, radial bar and v-shaped topologies. Special attention is given to the optimization strategy and three alternative ways of...
The simple three-phase inverter topology that is most widely used in electrical machine drive systems produces a large, high-frequency common-mode voltage. Through capacitive coupling, a fraction of this common-mode voltage typically appears on the machine’s shaft relative to ground. The shaft voltage can discharge through the bearings of the machi...
In this paper the analysis of unbalanced magnetic forces in magnetic gears are presented, based on which guidelinesforidentifyingsuitablepole-pairsandpole-piecescombinations for magnetic gear design with minimum unbalanced force are proposed. Furthermore, the vibration analysis is conducted on two prototype magnetic gears to evaluate the impact of...
This paper presents the 2D finite element analysis (FEA) based design optimization of a surface-mounted permanent magnet vernier machine (PMVM), and its comparison against the permanent magnet synchronous machine (PMSM) in a 15 kW wind generator application. The PMVM’s operating principle is briefly discussed, and attention is given to the selection...
In recent years, many interesting machine topologies based on the flux-modulation principle have been proposed. An attractive feature of these machines is the high torque density that can be realized. Many works in this field highlight the merits of a single topology. In this paper, the performances and material requirements of several different flux-...
This paper investigates the use of the Taguchi method for the design of line-start
permanent magnet synchronous motors (LS-PMSMs). To address the inherent limitation
of the Taguchi method in solving multi-response optimization problems, an improved regression rate methodology and a weighted factor multi-objective technique are incorporated to form...
In high power industrial applications such as air-cooled condenser fans, excessive mechanical gear failures highlight a need to investigate possible alternatives. In this paper the concentric magnetic gear (CMG) is evaluated as a potential replacement for traditional mechanical gear. For a more objective comparison between the CMG and mechanical ge...
Although cogging torque in magnetic gears (MGs) has been studied, the additional degree of freedom inherent to MGs makes it unclear exactly what is defined as the cogging torque of a MG. Although MGs generally have relatively smooth torque transfer characteristics, this paper reveals that when the gear is used in an up-speed configuration, cogging...
It is well known that the Newton-Raphson method is the most popular iterative method for nonlinear finite element problems. The method has a quadratic convergence. Under certain conditions on the Jacobian of the functional and the initial guess the Newton-Raphson method can converge very fast. However, standard evaluation of such Jacobian may not b...
There has been a considerable amount of research work on using the Taguchi method for
electrical machine design in recent years. However, for the large community of electrical machine
designers, this method is still less known. The purpose of this paper is to summarise the past and
current research work of applying the Taguchi method in electrical...
This paper investigates the use of the Taguchi method based regression rate optimization method for the design of line-start permanent magnet motors. A weighted factor multi-objective (MO) technique is used to take into account both steady-state and transient performance objectives. To validate the proposed method a prototype machine has been
desig...
In this paper the Taguchi method based regression rate method is proposed for optimising the
transient performance of line-start permanent magnet synchronous machines (LS-PMSM). To enable
the fast evaluation of the synchronisation capability of a design during the optimisation process, an
analytical LS-PMSM synchronisation model is used to determin...
Analytical magnetic field calculations are often used in the electrical machine design and
analysis. Since the solutions presented are generally in form of Fourier series without error estimation,
the numeric convergence and accuracy are not always guaranteed. In many cases higher number of
harmonic terms are required to obtain a satisfactory resul...
In this paper, the finite element analysis (FEA) based design optimization of a surface-mounted permanent magnet (PM) vernier machine is presented. The rapidly increasing weight and size of the machine is usually one of the major concerns in low operating speed directly driven wind turbine configurations. Hence, the total mass and volume are chosen...
Cogging torque in permanent magnet machines is undesirable because it is a source of noise and vibration
and because it has a negative impact on controllability. Over the years, many design techniques that can effectively reduce cogging torque have been developed. However, due to manufacturing tolerances, a machine’s cogging torque characteristics...
A main challenge in designing line-start permanent magnet synchronous motors is synchronization analysis and determination. The transient time-step finite element simulations are often required in the design process, which is computationally expensive. An attractive alternative is to use an analytical synchronization model, which is time efficient...
In this paper, an efficient energy-based methodology is proposed for calculating the torque performance of a novel magnetic planetary gear. To verify the proposed method and the gear performance, a prototype was also constructed and experimentally evaluated. It shows good agreement between the predicted and measured torque performance. The new gear...
In this paper, a magnetically geared permanent magnet (MGPM) machine is proposed for use in wind power generation. The structure layout, operating principles and equivalent circuit of the MGPM machine are first described. Then an efficient finite element method (FEM) based design optimization approach is formulated and implemented in the design of...
A main challenge in designing a line-start permanent magnet synchronous machine (LS-PMSM) is the synchronization analysis and determination. Often the use of time-consuming transient time-step finite element (FE) simulations is unavoidable in the design process. An attractive alternative is to use an analytical synchronization model, which is effic...
In this study a line-start reluctance synchronous machine (LS-SynRM) was designed and optimised using a finite element method based approach. Simulation results showed that the optimised LS-SynRM when compared to an induction machine achieved better efficiency, but lower power factor and higher torque ripple. Based on the simulation results, a LS-S...
Magnetically geared permanent magnet (MGPM) machines are an attractive alternative for wind power applications because of their merits over other machine types. A prototype MGPM machine was constructed in a recent study. Although both theoretical and finite element methods predict high efficiencies on the design, the prototype’s practical measureme...
This paper presents the design, construction, and experimental performance evaluation of an axial flux magnetically geared permanent magnet (MGPM) machine for wind power application. The optimum electromagnetic design for both magnetically coupled and decoupled configurations is described. Considering the complex structure of the axial flux MGPM ma...
This paper presents the design optimization and performance evaluation of an outer-rotor vernier machine with surface mounted permanent magnets. First the design specifications of the machine are described, then the design strategy and the optimization procedure are given in detail. A prototype based on the optimum design is manufactured and experi...
This paper presents the design and evaluation of a magnetically geared permanent magnet machine with an inner stator. A brief overview of relevant operating principles is first given. A simplified design and simulation methodology which can ensure that the magnetic gear and the stator are well matched, is then devised. The method is applied to the...
This paper investigates the transient synchronization performance of a line-start permanent magnet synchronous machine (LS PMSM) taking into account the effect of the rotor cage slot design, active permanent magnet volume and load inertia. First the transient performances of a rotor cage with different slot profiles and the same cross sectional are...
This paper investigates the transient synchronization performance of a line-start permanent magnet synchronous machine (LS PMSM) taking into account the effect of the rotor cage slot design, active permanent magnet volume and load inertia. First the transient performances of a rotor cage with different slot profiles and the same cross sectional are...
This paper presents the implementation of the Taguchi method for a retrofit design of a line-start permanent magnet motor. To evaluate the viability of the method, the optimum designs obtained from both the Taguchi and a traditional optimization methods are compared. This outlines the respective advantages and disadvantages of both methods. It show...
This paper presents the implementation of the Taguchi method for a retrofit design of a line-start permanent magnet motor. To evaluate the viability of the method, the optimum designs obtained from both the Taguchi and a traditional optimization methods are compared. This outlines the respective advantages and disadvantages of both methods. It show...
This paper presents the design, optimisation and prototyping of a 2.2 kW line-start permanent magnet synchronous motor. The initial design is done using analytical approach based on classical machine theory, which is then optimized. For the optimization, a gradient based Quasi Newton algorithm is used along with generic cost function methodology. T...
This paper investigates the use of the Taguchi method for the design and optimization of a line-start (LS) permanent magnet synchronous machine (PMSM). The method is implemented separately for the steady-state and transient performance optimization. The optimized machine shows good transient performance as well as the steady-state performance that...
The simulation of magnetically geared electrical machines using the finite element method is an especially demanding task when movement has to be considered. Several methods that facilitate movement exist. In this paper, two of these methods, the macro air-gap element (AGE) and the moving band (MB) are applied in a time-stepped static simulation of...
This paper is concerned with the design improvement of a previously designed magnetic gear with emphasis on performance optimization and the mitigation of end-effects. The performance analysis results show approximately 70% reduction in losses at full load and a 40% increase in maximum torque capability. New flux modulator manufacturing techniques,...
Magnetic gears and integrated magnetically geared machines have recently received much attention due to their exceptionally high torque densities. As in the design and analysis of conventional electrical machines, the finite element method (FEM) has been widely used for this class of electrical machine. For the sake of computational efficiency, the...
This paper reviews the historic and current development of magnetic gear technologies. There has been considerable amount of research and development activities on magnetic gear technologies in recent years. However, it is still not clear if this technology is ready for potential industry applications. The purpose of this paper is to summarize the...
This paper reviews the historic and current development of magnetic gear technologies. There has been considerable amount of research and development activities on magnetic gear technologies in recent years. However, it is still not clear if this technology is ready for potential industry applications. The purpose of this paper is to summarize the...
This paper presents a method for designing an LS-PMSM by dividing the design into sub-machine components. Each of the individual sub-machine components is then designed using several classical machine design principles. Once all the components have been designed they can be combined to form an LS-PMSM. The machine design is verified in two manners....