Trans-rotary Magnetic Gear Research Articles

Topology Optimization of the Reluctance Trans-Rotary Magnetic Gear

Advances in additive manufacturing have been paving the way for unconventional topologies in electromechanical systems. As such, topology optimization can be employed to uncover topologies that were once considered impractical. This article investigates enhancing the shear stress of the reluctance trans-rotary magnetic gear (TROMAG) by optimizing the topology of the gear’s variable reluctance component. Reluctance TROMAG is a strong contender for force-intensive linear motion applications where a long stroke is required. Topology optimization is performed on the reluctance TROMAG with radially magnetized permanent magnet (PM) configuration as well as with quasi-Halbach magnetized configuration. Results show that the use of elliptical iron teeth backed by non-ferromagnetic core can make a 40% increase compared to the shear stress of the conventional (rectangular teeth with iron core) reluctance TROMAG with radial magnetization. The Halbach-magnetized TROMAG with elliptical iron teeth backed by non-ferromagnetic core achieves the same shear stress as the conventional reluctance TROMAG with Halbach magnetization, and the use of lightweight non-ferromagnetic material for the variable reluctance component can make significant reductions in the total gear weight.

Comparison of Control Strategies and Electromechanical Devices for the Backpack Energy Harvesting System

This article provides a general overview on the control strategies and their implications for the backpack energy harvesting system. The control strategies include reactive control and resistive damping. The study is performed for three cases of electric generator: the direct drive linear generator, the rotary machine integrated with the trans-rotary magnetic gear (MITROMAG), and the rotary machine coupled with a mechanical rack and pinion (MRP). Equivalent circuits based upon electrical–mechanical analogies are employed to help understand the system dynamics under the two control strategies. It is shown that in all cases, upon reactive control, more power can be harvested; however, it comes at the cost of a higher velocity, peak power, and force requirement. Moreover, it is shown that for most of the operating points considered, the direct drive linear generator outperforms the geared electromechanical devices in terms of the harvested power. Furthermore, it is revealed that the low stiffness of the MITROMAG slightly increases its harvested power compared to the MRP under the resistive damping strategy.

Magnetic Design Aspects of the Trans-Rotary Magnetic Gear Using Quasi-Halbach Arrays

This article investigates magnetic design aspects of the trans-rotary magnetic gear (TROMAG) that using a quasi-Halbach array. TROMAG is a magnetic gear that converts high-force, low-speed linear motion to low-torque, high-speed rotational motion and vice versa. It is shown that quasi-Halbach magnetization significantly improves the force capability of the device compared to that of radial magnetization. Finite element analysis is used to study several design aspects of the quasi-Halbach TROMAG, including optimization of magnet dimensions and core thickness, effect of air gap length, effect of magnet remanent flux density, and distribution of flux density in the air gap. Moreover, the possibility of demagnetization is studied, and it is shown that if the quasi-Halbach TROMAG becomes overloaded repeatedly, demagnetization of magnets can degrade its force performance down to that of a similar TROMAG with radial magnetization. A quasi-Halbach TROMAG is prototyped, and static force and flux measurements verify the theoretical results.

Equivalent Circuit for the Trans-Rotary Magnetic Gear

This letter proposes an equivalent circuit for the trans-rotary magnetic gear. The circuit is presented for both impedance and admittance analogies. In both analogies, the gearing effect is modeled by a transformer. The gear's compliance is modeled by a parallel capacitor in the impedance analogy and by a series inductor in the admittance analogy. As an example, the proposed equivalent circuit is coupled to the equivalent circuit of a backpack energy-harvesting system to create an all-electric equivalent for the energy-harvesting system. The resulting all-electric equivalent circuit provides insight into system dynamics and control strategies. Moreover, the proposed circuit can be readily extended to other types of magnetic gears.

Leakage Flux of the Trans-Rotary Magnetic Gear

This paper investigates the leakage flux of the trans-rotary magnetic gear (TROMAG). TROMAG is a magnetic gear that converts a high-force low-speed linear motion to a low-torque high-speed rotation and vice versa. TROMAG is tailored to force-intensive linear motion applications such as backpack energy harvesting and artificial heart in which the gear is positioned close to the human body and/or electronic devices. In such applications, it is critical to ensure the TROMAG’s magnetic field penetrating the surrounding environment (referred to as the leakage flux hereafter) is below the limits permitted by standards. This paper employs 3-D finite-element analysis (FEA) to study spatial distribution and magnitude of the leakage flux. The FEA calculations of magnetic field are verified by experimental measurements. Both radial and quasi-Halbach configurations are investigated, and it is revealed that the quasi-Halbach configuration exhibits less leakage flux. Moreover, it is shown that the use of a thin iron shield surrounding the TROMAG can effectively reduce the leakage down to permissible values.

Control of an Electric Machine Integrated With the Trans-Rotary Magnetic Gear in a Motor Drive Train

This paper studies the dynamic performance of an electric machine integrated with the transrotary magnetic gear (MITROMAG) in a motoring mode of operation. MITROMAG is formed by mechanically coupling a rotary electric machine to the rotor of a trans-rotary magnetic gear (TROMAG). TROMAG is a magnetic device that, through magnetic fields, converts a low-torque, high-speed rotation of its rotor to a high-force, low-speed linear motion of its translator, and vice versa. In a motoring mode of operation, the rotor of the TROMAG is driven by a rotary electric motor, and as a result, its translator drives a reciprocating load. A nonlinear dynamic model is developed for the TROMAG. Oscillation tests are presented as examples of how the model can be used to predict the dynamic behavior of the device. The model is then linearized to derive system transfer functions and study the dynamic response of the MITROMAG to speed commands. Experimental results confirm the analysis.

Design and Analysis of a Shoe-Embeded Power Harvester Based on Magnetic Gear

This paper presents a shoe-sole-embedded power harvester which can extract power from walking to charge portable or mobile electronic devices. The core component of the design is a combination of a trans-rotary magnetic gear (TRMG) and a disk-type axial-flux permanent magnet (AFPM) generator. The key idea is to convert linear foot motion into rotation using the TRMG, so that the AFPM can be driven to generate electric power. The proposed energy harvester has a high power density due to its electromagnetic nature. Moreover, by integrating a TRMG, it eliminates the mechanical problems caused by the conventional transmission mechanisms, which also makes it compact in size. Besides introducing its structure and working principle, the design procedure is presented and its performance is analyzed using the finite-element method.

Guest Editorial Optimal Design of Electric Machines

The papers in this special section cover the advances in multi-objective design and optimization based on genetic algorithms, surrogate, polynomial regression, and particle swarm optimization techniques. Design of novel trans-rotary magnetic gear, hybrid machines for dc generation, and two degrees of freedom split-stator induction machines highlight new magnetic configurations and their performance evaluations. Multiphysics analysis of magnetothermal and magnetostructural behavior of Switched Reluctance Machine (SRM) and brushless doubly fed machines shed light on analytical and practical aspects of design in electromechanical converters. Finally, control of torque undulation, loss minimization, low speed high torque operation, and advanced digital control of adjustable speed motor drives conclude this unique collection of papers.

Design of an Electric Machine Integrated with Trans-Rotary Magnetic Gear

Design aspects of the trans-rotary magnetic gear (TROMAG) integrated rotary machine are discussed in this paper, with particular focus on optimizing system cost and weight. Analytical models are used for design of the TROMAG. Optimal designs of the rotary machine are found by using a population-based genetic algorithm and two-dimensional finite-element analysis and thermal considerations. Weight, volume, and cost of the resultant system are then compared with the Pareto-optimal set of a permanent magnet linear tubular machine that is designed for the same force and speed specification. It is shown in this paper that, for high-force low-speed reciprocating motion applications, an electromechanical motion system consisting of a TROMAG and a rotary electric machine can far surpass a conventional direct drive linear machine in terms of weight, volume, and initial and operating cost.

Magnetic Design Aspects of the Trans-Rotary Magnetic Gear

This paper studies several magnetic design aspects of the trans-rotary magnetic gear (TROMAG). The TROMAG is a magnetic device that converts linear motion to rotation, and vice versa, through magnetic field while doing a gearing action. This means that a high-force, low-speed translation can be converted to a high-speed low-torque rotation. Once coupled with a conventional rotary machine, the resultant system may be used as a compact electromechanical motion system for high-force linear-motion applications, such as wave energy conversion. The paper investigates the magnetic design of the TROMAG by means of either two-dimensional (2-D) or three-dimensional (3-D) finite element analysis (FEA), or an accurate analytical model. The impact of nonideal discretized helix and dimensions of magnets and air gap are investigated, as well as scaling rules of the TROMAG and the possibility of demagnetization. Experimental results obtained from a lab prototype are also presented to verify the concept and analysis.

Principles of the Trans-Rotary Magnetic Gear

This paper introduces the concept of the trans-rotary magnetic gear (TROMAG). The TROMAG is a magnetic device consisting of a rotor and a translator with an air gap in between, capable of converting linear motion to rotation, and vice versa, and doing the gearing action at the same time. Although its structure suggests that the TROMAG is simply the magnetic dual to the mechanical lead-screw, the authors show that the concept could also be derived from the elementary magnet arrays. The paper tries to establish an analogy between the TROMAG and the ordinary electrical machines with respect to the number of poles and the stack length, thus providing a deeper insight into the device operation. Three-dimensional (3-D) finite element analysis (FEA) is deployed to obtain the torque and force characteristics. Furthermore, it is shown that in addition to the permanent magnet (PM) TROMAG, developing the reluctance and the induction TROMAG is possible as well, but at a lower force density.