Wilhelm Peters

Monitoring critical temperatures in permanent magnet synchronous motors using low-order thermal models

Monitoring critical temperatures in electric motors is crucial for preventing shortened motor life spans due to excessive thermal stress. With regard to interior permanent magnet synchronous motors (IPMSM), critical temperatures typically occur in the magnets and in the stator end winding. As directly measuring temperatures, especially on the rotating part, is costly, sensitive and thus not applicable with respect to automotive applications, model-based approaches are preferred. In this paper, two low-order thermal models for accurate temperature estimations in the permanent magnets, the winding and the end winding are introduced and compared. The model parameters are estimated solely based on experimental data via a multistep identification approach for linear parameter-varying systems. The model performances are validated by extensive experimental results based on a high-speed PMSM typically used as traction motor in subcompact electric cars.

Discrete-time design of adaptive current controller for interior permanent magnet synchronous motors (IPMSM) with high magnetic saturation

IPMSM for automotive traction applications exhibits a rather high magnetic saturation as a result of the maximization of power and torque densities. Additionally due to the high speed range high electrical frequencies in proportion to the converter switching frequencies occur. That results in a small number of samplings per electrical fundamental. Both effects have to be taken into account to design a suitable current controller. In this paper a discrete-time IPMSM model considering parameter variations due to magnetic saturation as well as the effect of a small number of sampling instants per electrical rotation is derived. Then the design of an adaptive current controller is presented and evaluated by experimental results.

Optimum efficiency control of interior permanent magnet synchronous motors in drive trains of electric and hybrid vehicles

In automotive traction applications the interior permanent magnet synchronous motor (IPMSM) is preferentially chosen as traction drive due to its high torque and power densities. In drive trains of electrical vehicles (EV) and most hybrid electrical vehicles (HEV) the traction motor is operated in torque controlled mode. In a field-oriented control scheme an operation point selection strategy is required to choose appropriate current setpoints to generate the requested torque with high precision and optimal efficiency. In this paper the potential to improve the efficiency by operating a motor with minimum overall losses instead of minimum current per torque is investigated. The interaction between the motors loss characteristic, the impact of the voltage limit and the relevance of operation points for vehicle operation is explored theoretically and based on loss measurements. It is shown, that the losses can potentially be reduced at medium to high motor speeds with moderate torque requirements. This operation range corresponds to traveling with constant medium to high speed and slight acceleration and deceleration in electric vehicles. As well most operation points of the New European Driving Cycle (NEDC) and the Worldwide harmonized Light vehicles Test Procedure (WLTP) are in that operation range due to the moderate accelerations and decelerations in both driving cycles.

A precise open-loop torque control for an interior permanent magnet synchronous motor (IPMSM) considering iron losses

Interior permanent magnet synchronous motors (IPMSM) are preferentially chosen as traction drives for electric vehicles due to their high power and torque density. In a field-oriented control scheme an operation point selection strategy is required to choose appropriate current set points to generate the requested torque with high precision and optimal efficiency. Although the currents are controlled in terms of a closed-loop control, the operation point selection is an open-loop torque control. Thus a precise motor model considering the impact of saturation effects and iron losses is required to estimate appropriate current set points. This paper proposes a lookup-table (LUT) based operation point selection. The lookup-tables are generated offline using the Maximum Efficiency (ME) strategy considering saturation effects and iron losses.

Real-time capable methods to determine the magnet temperature of permanent magnet synchronous motors — A review

The permanent magnet synchronous motor (PMSM) is widely used in highly utilised automotive traction drives and other industrial applications. With regards to the device life-time, safe operation and control performance, the magnet temperature is of great interest. Since a direct magnet temperature measurement is not feasible in most cases, this contribution gives a review on state-of-the-art model-based magnet temperature determination methods in PMSM. In this context, the existing publications can be classified into thermal models, flux observers and voltage signal injection approaches. Firstly, brief introductions of these methods are given, followed by a direct comparison regarding drawbacks and benefits. Finally, this contribution concludes with an outlook of potential further investigations in this research field.

Voltage controller for flux weakening operation of interior permanent magnet synchronous motor in automotive traction applications

In electric automotive traction drives an optimal utilization of the DC-bus voltage in the wide flux weakening range is crucial. At the same time a voltage margin is required to ensure the stability of the inner current control loop. An adequate trade-off between these conflicting objectives is obtained by employing a superimposed voltage controller that is activated during flux weakening operation. In this paper, the design of such a voltage controller is presented. A simplified voltage controller plant model is identified from step response measurements. Due to variations of the plant parameters, the voltage controller is designed as a gain-scheduling controller with sufficient robustness towards plant model inaccuracies. The performance of the voltage controller is demonstrated by test-bench measurements based on an electric traction motor typically employed in sub-compact electric vehicles.

FPGA-based realization of self-optimizing drive-controllers

An FPGA (Field Programmable Gate Array) implementation and suitable power electronics can lead to a fast torque response in motion drive applications. However, when the controller parameters or its structure have to be adapted to internal and external varying conditions, e.g., when a self-optimizing control system is pursued, a static implementation might not lead to the best utilization of reconfigurable resources. This contribution outlines the implementation of a self-optimizing system composed of several possible hardware and software realizations of controllers for a permanent magnet servo motor. How well a specific controller realization is suited to the current situation is evaluated based on control quality and realization effort (i.e., CPU time, reconfigurable area). A System-on-Chip architecture is presented, which enables an on-line exchange of FPGA- and CPU-based realizations of controllers to optimize resource utilization and control quality. It is shown that by using dynamic hardware reconfiguration, such self-optimizing controller can be implemented based on FPGA technology. Furthermore, the design-flow including self-developed tools is outlined. Experimental results show that the proposed scheme works satisfactory.

Current controller with defined dynamic behavior for an interior permanent magnet synchronous motor

Typically traction and electronic stability programs (ESP) as well as drive train oscillation damping applications in electrical vehicles are realized in a cascaded control structure with the current control as innermost loop. The current control dynamic, however, is usually varying due to nonlinear effects as controller output saturation and changing motor parameters. In this paper a current control scheme is presented that ensures a well defined dynamic behavior despite these nonlinear effects. As a consequence, the design of superimposed control loops is simplified due to the well known linear dynamics, which in turn can be beneficial with respect to the performance of the entire control loop.

A critical review of techniques to determine the magnet temperature of permanent magnet synchronous motors under real-time conditions

The permanent magnet synchronous motor (PMSM) is widely applied in highly utilised automotive traction drives and other industrial applications. With regards to the device life-time, thermal utilisation, safe operation and control performance, the permanent magnet temperature is of great interest. Since a direct magnet temperature measurement is not feasible due to constructional and cost issues in most applications, this contribution gives a review on state-of-the-art model-based magnet temperature determination techniques regarding PMSM. In this context, the existing publications can be classified into thermal models, flux observers and voltage signal injection approaches. Firstly, brief introductions of these methods are given, followed by a direct comparison regarding drawbacks and benefits. This evaluation exhibits the individual constraints of each approach motivating their fusion as an outlook of further investigations in this research field.

Regelung elektrischer Traktionsantriebe in Elektro- und Hybridfahrzeugen

Zusammenfassung Für automobile elektrische Antriebe werden derzeit permanent erregte Synchronmaschinen favorisiert, die aufgrund der spezifischen fahrzeugspezifischen Anforderungen ein gegenüber Industrieantrieben deutlich anderes Verhalten aufweisen. Charakteristisch ist ein nichtlineares Reluktanzdrehmoment, eine starke magnetischen Sättigung und der sehr große Konstant-Leistungs-Bereich. Der Beitrag beschreibt die Strukturierung einer hierfür geeigneten Regelung mit der Auswahl des optimalen Arbeitspunkts, der unterlagerten Stromregelung und dem Umgang mit der die Reglerstellgrößen begrenzenden speisenden Gleichannung. Abstract Permanent magnet synchronous machines are currently the favorits as automotive electrical drives. Their behaviour, however, is considerably different from those of industrial drives due to the specific automotive requirements. Characteristics are a nonlinear reluctance torque, strong magnetic saturation, and a wide constant-power operation range. The paper descibes the structure of a suitable control, addressing the selection of an optimal operation point, the inner current control, and how to cope with the controller saturation due to the supplying DC voltage.