Encoder determines an angle of rotation of its own shaft. As a resolver is a rotary device, let's look only at rotary encoders. There are many encoder types according to operation and sensing principles. Manufacturers produce optical, magnetic, inductive, capacitive, resistive, and even mechanical types. Each of them has its own features. We have already described this in detail in the following article: Types of encoders.
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The variable reluctance (VR) resolver is usually used to measure the shaft angle of motor. A novel VR resolver with asymmetric teeth on the stator is proposed to achieve the minimal number of active teeth and eliminate the amplitude imbalance of the output voltages of SIN and COS coils by bringing the fifth compensating tooth. The structure and the total output voltages of signal windings are explicated theoretically in detail. The topology of such a machine just requires 2D finite element analysis (FEA) to accurately predict the machine performance. Results of FEA and principle of VR resolver with asymmetric teeth are in good agreement, and several special relevant problems are studied. Finally, experimental results validate the theoretical analysis and FEA of the proposed VR resolver.
This paper is organized as follows. Firstly, the construction and work principle of novel VR resolver with asymmetric teeth on the stator are introduced in Section 2. The expressions of air-gap permeance and the output voltages of signal windings are deduced. Section 3 shows results of FEA to validate the analysis of novel VR resolver with asymmetric teeth. Related problems including the difference between SIN and COS compensating coils and arbitrariness of the location chosen for the compensating tooth are emphasized. The prototype and test bench are developed based on the analysis and computation results above; the performance of VR resolver with asymmetric teeth is investigated in Section 4, including the output voltages of signal windings and zero-error. Conclusions are summarized in Section 5.
The SIN signal should be always in quadrature with COS signal, that is, the SIN winding and the COS winding must be mechanically displaced 90 electrical degrees from each other in the stator. And, the principle of slot-pole combination of VR resolver should be followed strictly. As a result, the number of teeth on the stator is selected as five; the rotor pole number is chosen as four and the angle-interval of the neighboring tooth on the stator should be 67.5 mechanical degrees. The structure of novel VR resolver with asymmetric teeth on the stator is shown as Figure 1.
Obviously, after the compensating tooth and compensating coils are proposed, the total output voltages of the signal windings will only contain fundamental component and vary with the rotation of the rotor strictly, which can naturally obtain a higher precision to a great extent. This is the principle of novel VR resolver with asymmetric teeth on the stator.
The following conclusions can be drawn from the analysis of the novel VR resolver with asymmetric teeth on the stator.(1)The fifth asymmetric tooth, nonactive, called compensating tooth, plays a pivotal role in the new topology of VR resolver. The induced voltages of compensating coils can eliminate the average value from the voltages of SIN and COS coils so that the precision will be improved substantially.(2)The calculated electric error of the proposed VR resolver can approach 0.7. Several relevant special issues caused by special construction are researched in detail. Computations of FEA are consistent with the principle analysis of the proposed VR resolver.(3)Experimental results show that the novel VR resolver has equivalent precision (0.5) compared with the same type of conventional top VR resolvers. However, it is confirmed that the novel VR resolver with asymmetric teeth on the stator is advantaged with reliability and cost due to the simple manufacturing process and structure of stator. It is more cost effective, so, as position sensor, it is very useful for low cost drives or electric vehicles.
Abstract:Rotor shaft position sensors are required to ensure the efficient and reliable control of Permanent Magnet Synchronous Machines (PMSM), which are often applied as traction motors in electrified automotive powertrains. In general, various sensor principles are available, e.g., resolvers and inductive- or magnetoresistive sensors. Each technology is characterized by strengths and weaknesses in terms of measurement accuracy, space demands, disturbing factors and costs, etc. Since the most frequently applied technology, the resolver, shows some weaknesses and is relatively costly, alternative technologies have been introduced during the past years. This paper investigates state-of-the-art position sensor technologies and compares their potentials for use in PMSM in automotive powertrain systems. The corresponding evaluation criteria are defined according to the typical requirements of automotive electric powertrains, and include the provided sensor accuracy under the influence of mechanical tolerances and deviations, integration size, and different electrical- and signal processing-related parameters. The study presents a mapping of the potentials of different rotor position sensor technologies with the target to support the selection of suitable sensor technologies for specified powertrain control applications, addressing both system design and components development.Keywords: automotive electric powertrain; permanent magnet synchronous motor; rotor position sensor; resolver; inductive position sensor; eddy current position sensor; Hall sensor; magnetoresistive position sensor
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