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This paper proposes a position sensorless control technique for permanent magnet synchronous motor (PMSM) used in rail transit application, where a segmented synchronous modulation (SSM) is usually applied. The arbitrary signal injection-based sensorless control is adopted to estimate rotor position. In a switching period, an oversampling technique is used to obtain the average current slope that contains the rotor position information during the active voltage-vector operation. In SSM, the hysteresis zone is set near the carrier ratio (CR) switching critical point to eliminate the influence of the repeated oscillation on the current measurement accuracy. Furthermore, a load disturbance compensation method is designed so that the failure of hysteresis zone is avoided. Through the analysis of power spectral density (PSD) of phase current, the optimization of harmonic energy distribution with hysteresis zone is also verified. The experimental results show that the proposed method can improve the position estimation precision during the fast CR transition, which can be effectively applied in SSM. INDEX TERMS Permanent magnet synchronous motor (PMSM), segmented synchronous modulation (SSM), arbitrary signal injection, oversampling, sensorless control.

This study proposes an integration design of sensorless closed-loop drives for rail transit application employing interior permanent magnet synchronous machine (IPMSM), which works under low switching frequency. Due to the long signal sampling period in high-speed region, the individual back-EMF observer cannot ensure the sensorless closed-loop control stability. In order to increase the speed dynamic response and decouple the d-q axes currents accurately, a fast non-singular terminal sliding mode control is designed. It combines a linear sliding mode factor with conventional non-singular terminal sliding mode and is applied uniformly to position observer, speed and currents regulators. Then, considering the effect of inverter nonlinearity on position observer, the observed position error caused by dead-time is analysed, and a compensation method based on q-axis voltage error is proposed. Based on the above methods, a comparison analysis of position observer, speed and currents regulators is given. Finally, a 3.7 kW IPMSM is tested to verify the feasibility of the improved sensorless method. Nomenclature i dq i dq * actual (given) stator current along d-axis(q-axis) of the rotor flux, A i αβ i^α β actual (estimated) stator currents of αβ-axes, A ω r ω r actual (estimated) value of electrical angular velocity, RPM L d L q stator inductance of d-axis(q-axis), H R s stator resistance, Ω ψ f rotor permanent magnet flux linkage, Wb u dq stator voltage along d-axis(q-axis) of the rotor flux, V u αβ stator voltages of αβ-axes, V e λ e^λ extended electromotive force (estimated value), V T L T^L load torque (estimated value), Nm T e T^e electromagnetic torque (estimated value), Nm p and q positive odd numbers and satisfy 1 < p/q < 2 γ, ε and η design parameters for the sliding mode control law, positive L linear gain factor, as shown in (8) D differential operator