Abstract：The speed-sensorless induction motor drives (SSIMD) technique possesses high reliability, easy maintenance, low cost, and is adopted broadly. High performance of the SSIMD system relies on the precise rotor speed information. Recently, several papers have been reported to realize speed estimation as accurate as possible. For the SSIMD control system, the feedback matrix of the adaptive full-order observer (AFO) can theoretically reduce the unstable regenerating region, and improve the speed estimation performance in low-speed regenerating mode. However, the desired performance of existing methods deteriorates at low stator frequencies due to parameter uncertainties. The boundaries of the unstable region cannot coincidence with the inevitable parameter uncertainties. Actually, most of existing methods ignore the flux error, which is unable to be observed directly by instruments. Then the necessary conditions of the SSIMD control system cannot be satisfied at the low-speed regenerating mode. To solve the problem above, this paper proposes a feedback matrix design method. To design and select the robust feedback in Section Ⅲ, a flux error online estimate method is introduced in Section Ⅱ based on decoupling error terms. Existing literature points out that both the stator current error and the rotor flux error are composed of stator resistance error, rotor resistance error, and rotor speed error. Hence, the expression of the flux error can be obtained by the decoupling analysis. To determine the weight coefficients, variations of ratios N1 and N3 against different synchronous speeds and torque currents are presented. Then the weight coefficients can be selected appropriately. Introducing the flux error into the feedback matrix design, the mathematical model and the block diagram of the control system with the proposed feedback matrix design are given in Section Ⅲ. To realize the necessary conditions of the SSIMD, the stability function of the AFO is reconstructed as a parabola. The function maximums and the robustness improvement design are discussed based on the vertex movement. With a constant term from the flux error, the stability of the SSIMD in the low-speed regenerating region can be guaranteed even if there are parameter uncertainties. The proposed method overcomes the sensitivity against parameter variation and enhances the robustness of AFO. Finally, the effectiveness of the proposed method is verified on a 2.2 kW IM experimental setup. Two identical machines are set to provide desired load torque and test the proposed method, respectively. In the load step experiment, the SSIMD control system operates stably with the proposed feedback design, when the stator frequency is 0.4 Hz. The conventional method fails to provide stable speed estimation at 0.6 Hz. The comparison experiments validate the superiority of the proposed method. To test the operation performance in the whole low-speed ranges, the speed reversal experiments are carried out. With the proposed feedback gains, the induction motor crosses the zero-stator-frequency line successfully with great speed observability. Furthermore, this paper shows the excellent speed tracking performance of the SSIMD control system using the loaded speed step experiments. The parameter robustness, as the core innovation in this paper, is validated by stator and rotor mismatches experiments. Although there are little observation errors, the control system works well. As conclusion, This paper has provided an alternative solution to enhance the stability of AFO, and also to realize the robustness of feedback gains against parameter uncertainties. The flux error has been estimated with the weight values derived according to IM operating conditions. On this basis, the current and the flux error are adopted as state variables of feedback gains term to design the multiple error-based feedback gains. The effectiveness has been confirmed by experiments in low-speed regenerating region. The stable operations have been realized against parameter uncertainties.
杨凯, 李孺涵, 罗成, 徐智杰, 郑逸飞. 考虑参数误差的无速度传感器异步电机低速发电工况稳定性提升策略[J]. 电工技术学报, 2023, 38(21): 5738-5748.
Yang Kai, Li Ruhan, Luo Cheng, Xu Zhijie, Zheng Yifei. Enhanced Stability for Speed-Sensorless Induction Motor Drives in Low-Speed Regenerating Region Considering Parameter Uncertainties. Transactions of China Electrotechnical Society, 2023, 38(21): 5738-5748.
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2023, Vol. 38 
