开关磁阻电机转矩控制

Abstract—In this paper the authors present a comparison between optimised versions of three torque sharing functions, with different number of degrees of freedom, used for improving the efficiency in Switched Reluctance Motors. Starting from the basic rectangular variation, the ascending and descending flanks of the function are modeled using a cosine, exponential and a more general approach (further referred to as piecewise cubic sharing function). The degrees of freedom varying between two and an arbitrary number (for the general approach) are determined so as to minimize losses, when operating in smooth torque conditions. Based upon an optimisation procedure with both linear and nonlinear constraints, the total (copper and iron) losses are minimized considering a limited available DC bus voltage. Moreover, a smooth model is presented so as to be able to separate the two main causes for the torque ripple and it is shown that, neglecting the chopping ripple, a ripple-free torque can be obtained. Extensive studies have been conducted for determining the optimal number of degrees of freedom (DoFs) for the piecewise cubic function. The proposed methods were successfully implemented on a 8/6, 30kW peak power, SRM both numerically and experimentally-wise.
the so-called, torque sharing functions (TSFs) [3], [4]. One of the advantages of EVs as compared to the ICE based vehicles is the high torque capability at low speed [9]. Moreover, for EV applications, it is important to reduce, or completely eliminate the torque ripple at low speed, as they generate low-order frequencies which along with the eigenfrequencies of the drivetrain can lead to mechanical resonance. Therefore, producing high torque for low ripple content is one of the main requirements of an electric motor used in EV propulsion [10]. The total torque can be produced by maximum two neighbour phases in SRMs with four-phases or less. At each rotor angular position, the share of each phase can be determined using an appropriate function for modelling the ascending and descending flanks of the basic rectangular variation. One of the first application of such a function is reported in [5] where an exponential variation is considered, followed by the authors in [6] where a cosine function is introduced. From the same category of nonlinear sharing functions, authors in [7] use a cubic variation. Although the ripple content is significantly reduced there is no attention paid to other quantities such as iron or copper losses. In [8] the functions presented in [5] to [7] are optimised for two objective functions: the rate of change of flux linkage and the copper losses. In this paper the optimised versions of the functions provided in [5], [6] are compared with generalized version of the cubic function (with an arbitrary number of DOFs), further referred to as piecewise cubic. Furthermore, the latter mentioned sharing function is tested by adding the iron losses in the optimisation. Thus, in this paper as performance indicators, copper and iron losses are used along with the extension of the torque-speed region from the torque-speed plane in which smooth torque can be produced. It is shown that the proposed piecewise cubic method allows for the production of smooth torque for a wider torquespeed range than other presented methods, as well as an
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J. Gyselinck2
Universit´ e Libre de Bruxelles BEAMS Dpt., Energy Group 50, F. Roosevelt Av., B-1050 Brussels, Belgium Email: johan.gyselick@ulb.ac.be
I. I NTRODUCTION Due to their undeniable advantages, SRMs represent a serious competitor for AC permanent magnet synchronous and induction machines used in hybrid and full electric vehicles, (HEVs/EVs), propulsion. Their main drawbacks are extensively mentioned in the literature [1] - namely, noise vibration and harshness problems (NVH), low efficiency and high torque ripple. This paper deals with the latter two problems. Besides the improvements that can be done at the machine design level, the control technique that is used plays a fundamental role in overcoming the two mentioned drawbacks. Moreover, for EV applications, wide speed range, highlydynamic, controllers are required, which in regular basis combine two torque control techniques embedded in a speed control loop [2]. One example would be an optimal firingangle based control scheme, where at low speed the ripple of the torque is minimized by means of current profiling using