Enhanced Stability for Speed-Sensorless Induction Motor Drives in Low-Speed Regenerating Region Considering Parameter Uncertainties

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 power (CHP) units by 26.43 WM. The centralized scheduling of IEHSs requires disclosure of all information privacy, such as topology structure, operating status, and network parameters. In contrast, EPNs and DHSs only need to communicate with 115 feasibility or optimality cut plants in a distributed way based on Benders decomposition. The total cost of EPNs in the combined heat and power optimal scheduling is decreased by $10 809 compared to the separate dispatch, but the total cost of DHSs is raised by $787. As a result, DHSs have no incentive to cooperate with EPNs. To promote cooperation, EPNs and DHSs redistribute cooperative surplus through Nash bargaining. The overall cost of EPNs is lowered by $5 011 compared to separate dispatch, and the total cost of DHNs is decreased by $5 011 compared to separate dispatch. According to the simulation results for the large-scale system, EPNs and DHSs only need to interact with 2 765 feasibility or optimality cut plants instead of disclosing 10 440 constraints. The overall cost of EPNs and DHNs are both decreased by $41 865 by sharing the cooperative surplus through Nash bargaining. The following conclusions can be drawn from the simulation analysis: (1) Combined heat and power dispatch considering pipeline energy storage can improve the flexibility of EPSs and reduce wind curtailment. (2) Compared with centralized scheduling, the distributed optimal dispatch for IEHSs based on Benders decomposition can fully protect the information privacy between EPSs and DHSs. (3) The proposed IEHS decentralized dispatch method based on Nash bargaining can decrease the total cost of EPSs and DHSs, respectively. © 2023 Chinese Machine Press. All rights reserved.