Abstract：Due to the asymmetric state of the five-phase fault-tolerant permanent magnet synchronous motor (PMSM) under open-circuit fault conditions, the operating performance with sensorless control is not satisfied. The estimated accuracy of rotor position deteriorates since the back electromotive forces (EMFs) estimated by traditional observers contain DC bias and high-order harmonics under open-circuit fault conditions. Therefore, a novel sensorless control strategy based on a rotor-flux observer was proposed. Firstly, based on the fault-tolerant model, a sliding mode observer (SMO) according to the exponential approach law was established to estimate back electromotive forces (EMFs). However, they contain dc bias, and low and high-order harmonics, which seriously affect the estimated accuracy of rotor position. Secondly, an improved second-order generalized integrator (ISOGI) was designed. The ISOGI transfer function can be expressed as $ \frac{\hat{\boldsymbol{\psi}}_{\mathrm{rs}}(s)}{\boldsymbol{V}_{\mathrm{s}}(s)}=\frac{k_{1} s^{2}}{s^{2}+k_{1} \hat{\omega}_{\mathrm{r}} s+\hat{\omega}_{\mathrm{r}}^{2}} \cdot \frac{k_{2} \hat{\omega}_{\mathrm{r}}}{s^{2}+k_{2} \hat{\omega}_{\mathrm{r}} s+\hat{\omega}_{\mathrm{r}}^{2}} \boldsymbol{Q}_{\mathrm{s}}$ (1) Combined with the SMO, the ISOGI was adopted to design a new rotor-flux observer. Then, a phase-locked loop (PLL) extracted the rotor position information from the rotor flux. Finally, the faulty PMSM can operate smoothly with a fault-tolerant method. Simulated results on the parameter robustness show that when the resistance, inductance, or permanent magnet flux becomes 0.5 and 2 times the actual parameters, the estimated errors of position and speed are almost unchanged. Thus, whether the parameters become larger or smaller, the estimated errors are almost the same as those under healthy conditions. An experimental platform was estimated to verify the feasibility and effectiveness of the proposed strategy. Steady-state experiments show that the maximum rotor position errors estimated by the SMO+SOGI and SMO+ISOGI are 0.55rad and 0.22rad, respectively. When reference speed changes, the maximum speed regulation time with the SMO+ISOGI strategy is 0.5s, while the SMO+SOGI strategy is 0.55s. When loads change, the maximum speed regulation time with the SMO+ISOGI strategy is 0.5s, while the SMO+SOGI strategy is 0.75s. The comparison between the SMO+SOGI and SMO+ISOGI strategies shows that the proposed strategy can reduce the estimated error of rotor position and improve the steady-state and dynamic performance under open-circuit fault conditions. The following conclusions can be drawn. ① Compared with the SMO+SOGI strategy, the proposed strategy has a strong filtering ability for DC bias, low and high order harmonics, effectively reduces the influence of open-circuit fault on estimated accuracy of rotor position, and improves the estimated accuracy of rotor position. Meanwhile, it has good steady-state and dynamic performance. ② Combined with the SMO based on the exponential reaching law, the proposed strategy can reduce sliding mode chattering and show good parameter robustness. ③ The proposed rotor flux observer based on the SMO+ISOGI can be applied for the sensorless control of PMSM under healthy and open-circuit fault conditions. ④ If two-phase open-circuit faults occur, the proposed rotor flux observer can achieve sensorless control based on a fault-tolerant control strategy.
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2023, Vol. 38 
