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| A Dual-Sampling Differential Position Decoding Method for Resolvers |
| Wu Chun, Ying Wangrui, Zheng Luhua, Cheng Fengmin, Zhi En |
| College of Information Engineering Zhejiang University of Technology Hangzhou 310023 China |
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Abstract Resolver decoding chips are usually used to obtain the rotor position in high-reliable applications, such as electric vehicles, robots, aerospace, etc. Nevertheless, there are some defects of high cost and complex peripheral circuits, which restrict wide applications in compact and low-cost driver systems. In recent years, some software decoding methods of resolvers have been proposed, but most of them suffered from extra components and low precision due to bias drift of sineand cosine signals. To address these issues, this paper proposes a dual-sampling differential position decoding method for resolvers. By sampling peaks and bottoms of the output signals of resolvers twice in one excitation period, the influence of bias drift of sine and cosine signals on the sampling accuracy is eliminated and the position decoding accuracy canbe improved.
Firstly, the main control chip generates a fixed PWM signals, such as 8 kHz in the paper, which are amplified to excite the primary windings of resolvers. Secondly, after processing the sine and cosine signals generated by the secondary windings of resolvers through the signal processing circuits, the sine and cosine envelope signals required by the software decoding are prepared. Thirdly, a differential dual sampling of the peaks and bottoms of the signal envelopes can increase the amplitude of the signals by onetime and eliminate the influence of the bias voltage of sineand cosine signals. Finally, a second-order PLL is adopted to track the rotor position of the resolvers in comparison with a third-order PLL and arctan function.
The results of dual-sampling position decoding and single-sampling position decoding methods are compared with the actual position measured by a 2 500-line photoelectric encoder. It is found that under the condition of 600 r/min, the position error of the dual-sampling method is within ±1.5° and that of the single-sampling method is within ±5.4°, which proves that the dual-sampling differential position decoding method has better steady-state performance. In the acceleration and deceleration experiments from standstill to 3 000 r/min, the maximum position errors during the acceleration and deceleration processes of the dual-sampling method are 7.5° and -7°, respectively. Meanwhile the errors of the single-sampling method are 9° and -8°, respectively. Moreover, the dual-sampling method has smaller phase current, which proves that the proposed dual-sampling differential position decoding method has better dynamic characteristics. Furthermore, in the low-speed and high-speed experiments of 20 r/min and 5 100 r/min respectively, the position errors of the dual-sampling method are within ±2° at low-speed, and those in the high-speed are -0.6° to 1.3°. In comparison, at the same conditions, the position errors of the single-sampling method are between ±10.8° and -5° to 8°, respectively. This proves that the dual-sampling differential position decoding method has better position tracking accuracy in full-speed range. In addition, the tracking performances of the second-order PLL, a third-order PLL and arctan function are compared in terms of steady-state accuracy and dynamic accuracy.
The experimental results show that: (1) The proposed dual-sampling differential position decoding method can reduce the influence of bias voltage on the output signals of resolvers, improve the signal-to-noise ratio of sine and cosine signals, and increase the update frequency of position decoding. (2) Compared with the conventional single-sampling method, the proposed method is robustness to the environment changing, and has better steady-state and dynamic performances with higher position tracking accuracy in full-speed range.
To sum up, the proposed decoding method is a high-performance software position decoding strategy and can replace the resolver decoding chips in main applications.
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Received: 26 June 2023
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2024, Vol. 39 
