Uwe Schäfer

Optimized Design of High-Speed Induction Motors in Respect of the Electrical Steel Grade

This paper presents the design of highly efficient high-speed induction motors with optimally exploited magnetic materials. First, new combined numerical-analytical design methods are presented and validated, which closely relate to the classical way of machine design but allow the designer to precisely account for material properties. Second, it is shown how two optimized 20-kW 30 000-r/min induction machines have been realized, i.e., one incorporating cobalt-iron alloy, and the other one using siliconized steel. Finally, the influence of the electrical steel grade on their performance is evaluated on the basis of electrical, thermal, vibrational, and noise measurements.

Comparison of high-speed induction motors employing cobalt-iron and silicon electrical steel

This paper presents the design of 20 kW cage rotor induction machines operating at speeds above 20.000 rpm employing different kind of electrical steels. One machine is designed using cobalt-iron laminations of 0.2 mm thickness. For the second machine 0.35 mm silicon electrical steel of low-loss grade has been used. Both machines are compared in terms of the materials influence on lamination layout, mechanical behavior and thermal loading. Measurements of both machines underline the presented facts.

Mass producible optimized BLDC motor for automotive dynamic pump applications

This paper addresses the key technical issues related to the design of a mass producible optimized BLDC drive for high pressure and dynamic automotive pump applications. The focus is on the electromechanical design of such a device for electro hydraulic suspension systems and other high pressure automotive pumps for the new 48V automotive standard for auxiliary drives. The motor comprises a fully encapsulated rotor and separated teeth for mass production.

An accurate magnetic characteristics measurement method for switched reluctance machines

Knowledge of magnetic characteristics is very important for the optimal control strategies of SRM drive system [1],[2]. There are several methods to determine the magnetic characteristics such as indirect and direct methods with DC or AC voltage supplies. However, each of methods has limitations or drawbacks in determinations of computation time, inductance saturation features and an influence of iron losses. In the accurate inductance profile method [3], the magnetization characteristics were calculated only in rising current and saturation zone. In this paper, the magnetization characteristics have been determined in three periods (rising, falling and saturation currents). Therefore, the measurement results are more accurate. Because the magnetization curves were calculated by averaging the rising and falling flux curves, the influence of iron losses is very small. The static magnetic characteristics obtained with this measurement technique have been verified under dynamic conditions [6]. The energy conversion loops in chopping current control were enclosed the magnetization curves from unaligned to aligned rotor positions. The results computed by finite-element magnetic method FEMM are compared with the experimental results. The magnetization characteristics obtained in measurement and FEA methods were used to simulate the nonlinear model of the three phase 30 kW, 50.000 rpm 6/4 SRM for aircraft starter/alternator.

Performance improvement of direct torque control for doubly fed induction generator with 12 sector methodology

Direct Torque Control (DTC) is a control technique which is commonly used for speed control of induction machine drives. Compared with the available control techniques, DTC is characterized by controlling the torque and the rotor flux directly without the use of current or voltage regulators, coordinate transformation, and PWM control technique. Though its simplicity in design, it achieves good control of the torque. Nevertheless, the hysteresis band in DTC produces ripples in flux and torque. In this paper, a comparison of conventional DTC scheme and the twelve sector DTC methodology for a doubly-fed induction machine (DFIG) is implemented according to the output torque ripple. Simulation results show the performance improvement of the twelve sector methodology over the conventional DTC technique. The simulations are performed in MATLAB / SIMULINK environment.

A virtual rapid analysis model for DC motors with single tooth windings

In this paper a virtual model for DC motors with single tooth windings and mechanical commutation is presented. The model permits the calculation of the physical values which are otherwise not measurable during actual motor operation while considering the non-linearity of a magnetic circuit. Coil values (current, voltage, flux linkage) and motor values (current, voltage, speed and torque) are both calculated very quickly and with high accuracy. The model utilizes a combination of data tables and simultaneous computations by two separate software programs. A comparison with test data and FEA calculations verifies the models accuracy. This model can be used to optimize parameters such as brush angle shift, number of turns, or geometric design. The relative speed of this calculation verses the conventional method is an inexpensive alternative for research and development.

Loss minimization algorithm of an IPMSM based on analytical expressions

This report presents an algorithm for reference current calculation to minimize losses in electric vehicles with PMSM. The algorithm calculates the current set points explicitly through analytical expressions depending on the requested torque, the speed of the drive and the available DC voltage. The required machine parameters have been gathered from experimental data.

Calculation of nonlinear flux linkage and torque for permanent magnet DC motors

This paper presents a virtual rapid analysis model (VRAM) replacing the conventional reduced order systems model for physical value calculation of permanent magnet DC brush motors. The VRAM accomplishes calculations while considering magnetic circuit saturation. Dynamic coil (current, voltage, flux linkage) and motor values (current, voltage, speed and torque) are calculated quickly and with high accuracy. In former research, the VRAM utilized 1D look-up tables to calculate each coils flux linkage, whereas this paper investigates enhanced magnetic circuit computation with 2D tables. This new method enables the virtual work principle to compute the torque more accurately for high motor currents. Nonlinear flux linkage and torque values are almost identical to validated 3D finite element analysis, therefore verifying the models accuracy. The VRAM can be used to optimize nonmagnetic parameters, determine torque curves or develop control algorithms. The VRAMs relative calculation speed versus conventional methods is an inexpensive alternative for research and development.

Implementation of DTC for IPMSM with FPGA considering field weakening operation

In this paper, a whole design of FPGA (Field-Programmable Gate Array) based control system for IPMSM (Interior Permanent Magnet Synchronous Motor) is presented. The IPMSM is now widespread for traction drive applications of electric vehicles (EVs) because of its high torque per volume ratio. In a DTC (Direct Torque Control) drive, flux linkage and electromagnetic torque are controlled directly and independently of each other by the selection of optimum inverter switching modes. In this contribution a DTC system is proposed to cope with efficiency optimization, limitation of the starting current and field weakening. The proposed DTC system utilizes the maximum-torque-per-flux (MTPF) method for efficiency maximization and a method for limiting the starting currents.

Low voltage ride through of doubly fed induction generator in wind power generation using crowbar solution

The main advantage of the doubly fed induction generators (DFIG) over the synchronous generators is the small size converter which is located in the rotor circuit. However, this advantage can cause a problem during grid faults, because the over voltages and currents that will occur on the rotor circuit can damage the rotor side converter (RSC), if it is not over-dimensioned or protected for such high voltages and currents. Crowbar protection is a quite common solution of the grid faults for DFIG, the crowbar connects small resistances to the rotor terminals of the generator in order to limit voltage and current peaks; the RSC is disconnected as long as the crowbar is active. In this situation the DFIG is still connected to the grid and support it with a reactive power to fulfill the grid codes. A simulation study of different types of grid faults will be carried out in MATLAB/SIMULINK environment.