Alexander Smirnov

Non-contact rotor position sensors are an essential part of control systems in magnetically suspended high-speed drives. In typical active magnetic bearing (AMB) levitated high-speed machine applications, the displacement of the rotor in the mechanical air gap is measured with commercially available eddy current-based displacement sensors. The aim of this paper is to propose a robust and compact three-dimensional position sensor that can measure the rotor displacement of an AMB system in both the radial and axial directions. The paper presents a sensor design utilizing only a single unified sensor stator and a single shared rotor mounted target piece surface to achieve the measurement of all three measurement axes. The sensor uses an inductive measuring principle to sense the air gap between the sensor stator and rotor piece, which makes it robust to surface variations of the sensing target. Combined with the sensor design, a state of the art fully digital signal processing chain utilizing synchronous in-phase and quadrature demodulation is presented. The feasibility of the proposed sensor design is verified in a closed-loop control application utilizing a 350-kW, 15,000-r/min high-speed industrial induction machine with magnetic bearing suspension. The inductive sensor provides an alternative solution to commercial eddy current displacement sensors. It meets the application requirements and has a robust construction utilizing conventional electrical steel lamination stacks and copper winding.

High-speed (HS) electrical machines provide high system efficiency, compact design, and low material consumption. Active magnetic bearings (AMBs) bring additional benefits to the HS system, such as elimination of the friction losses, reduced wear and maintenance, and a built-in monitoring system. HS drivetrains are usually designed for specific applications and require a high level of integration. This paper describes a design method of the HS electrical machine supported by AMBs, considering their mutual influence on the system performance. The optimization procedure, which takes into account both the electrical machine and bearing designs, is developed. The optimization is based on a multiobjective genetic algorithm. The selected optimization parameters include the AMB and machine dimensions. The optimization objectives cover the electrical machine performance and the rotordynamics. The results of the proposed optimization algorithm are implemented in the constructed 350-kW, 15 000-r/min induction machine with a solid rotor supported by AMBs. The prototype tests verify the design and optimization results.

Two-stage oil-free centrifugal air compressors can bring significant advantages and open new market opportunities for compressor manufacturers. One of the core technologies behind this compressor type is the high-speed electrical machine supported by active magnetic bearings. In this paper, the requirements set by the compressor on the electrical machine design are presented. The design solutions aimed to satisfy these requirements are discussed. Two case studies illustrate possible design approaches for the target application with examples of a 120-kW, 60 000-r/min induction machine with a solid rotor and a 225-kW, 50 000-r/min permanent-magnet synchronous machine (PMSM) with a full cylindrical magnet. The system design and simulation results are confirmed by measurements of a PMSM prototype.

Decentralized power and heat generation is a growing trend throughout the world. In smaller applications, electrical power output less than few megawatts, reciprocating engines have dominated the market. In recent years, small sized gas turbines have emerged as challengers for the reciprocating engines. The small gas turbines have a growing share of the decentralized energy market, which itself is rapidly growing. Hence, improvements in small gas turbine efficiency have a significant impact from the economic and environmental perspective. In this paper, the design of a high efficiency 400 kW gas turbine prototype is described and discussed. The prototype is a two-spool, recuperated and intercooled gas turbine where both spools comprise of a radial compressor and turbine, a permanent magnet electric generator, an axial and two radial active magnetic bearings and two safety bearings. The prototype design was divided into five categories and each of the categories are discussed. The categories were: the process design, the turbomachinery design, the generator and electrical design, bearing design and rotor dynamic analysis, and mechanical design. The design of recuperator, intercooler, and combustion chamber were outsourced. Hence, they are not discussed in this paper. The prototype design process showed the readiness of the chosen technological selections, as well it showed that the type of machine under discussion can be designed and manufactured.

A method is presented for tool tracking in active magnetic bearing (AMB) spindle applications. The method uses control of the AMB air gap to achieve the desired tool position. The reference tracking problem is transformed from the tool coordinates into the AMB control axes by bearing deflection optimization. Therefore, tool tracking can be achieved by an off-the-shelf AMB controller. The method is demonstrated on a high-speed AMB boring spindle with a proportional integral derivative (PID) control. The hypothetical part geometries are traced in the range of 30 μm. Static external loading is applied to the tool to confirm disturbance rejection. Finally, a numerical simulation is performed to verify the ability to control the tool during high-speed machining.

The authors wish to make the following corrections to this paper [1]: Figure 7 on page 3573 should be changed from:

A method is presented for tooltip tracking in active magnetic bearing (AMB) spindle applications. The proposed tool tracking approach uses control of the AMB air gap to achieve the desired tool position. A μ-synthesis-based controller is designed for the AMBs with the goal of robustly minimizing the difference between the tool reference and estimated tool position. In such a way, the model-based control approach concurrently addresses the tracking problem and the inability to directly measure real-time tool position in the presence of machining disturbances. To ensure the tractability of the control problem, a model of the desired tracking dynamics is included in the plant. The method is demonstrated on a high-speed AMB boring spindle. To confirm the tool tracking capability, characteristic part geometries are traced including stepped, tapered, and convex profiles. Tool tracking is demonstrated for the rotating AMB spindle in the range of 90 μm. Also, static and dynamic external loading is applied to the spindle tool location to confirm the disturbance rejection ability of the closed-loop system.

Active magnetic bearings (AMBs) are becoming very popular in high speed electrical machines applications in the last decade. As the interest in them grows the necessity to optimise all the aspects of their operation arises. This paper presents the analytical way of calculating losses of active magnetic bearings based on reluctance network method. The method provides fast estimation reducing development time and effort with accurate results. In the article the proposed method is compared with other popular losses estimation methods and verified with experimental results.

The hybrid system approach is used to minimize losses in the AMB system by switching controllers and bias current. The method is validated with experimental results at steady state and rotating system. With high bias orbits of the rotor are reduced while in the absence of disturbance the losses are minimized with low bias. The switching rules based on inner variables of the control system are proposed.