This paper proposes an integrated method of three-phase ac excitation and high-frequency voltage signal injection (HFVSI) for sensorless controlled starting of brushless synchronous machines (BSM) used as starter/generator in variable frequency ac power systems of civil aircraft. Fixed 400 Hz of the three-phase ac power is adopted both for the ac excitation and HFVSI in the initial starting process to eliminate the bulky rotor position sensor for BSM. The resulting 6th sequence harmonic voltage determined by the rotating rectifier is utilized as the HFVSI into the field-winding of main generator without any extra high-frequency signal injection. The rotor position is estimated by the high-frequency response signals extracted from the armature windings of main generator. Due to the nonlinear rotating rectifier linked in the HFSI chain, a novel frequency-insensitive asynchronous demodulation strategy is proposed in this paper for rotor position estimation. Furthermore, the initial rotor position detection is calibrated by polarity decision of the induced currents of the armature windings within the establishment procedure of field current of the main generator at standstill. The effectiveness of the ac excitation and feasibility of rotor position estimation for sensorless starting control of BSM are validated by the simulation and experimental results.

Model-based sensorless field-oriented control (FOC) suffers from overparameterization and can be laborious to use for a five-phase permanent magnet synchronous motor. On the other hand, insulated gate bipolar transistor (IGBT) frequently fails in an electric drive. Under IGBT failure, a freewheeling current is observed, and, above all, it carries the failed phase back electromotive force information. Based on this observation, this article presents the design of a brand new sensorless FOC by exploiting the freewheeling current to accommodate both IGBT and position sensor failures, which is expected to further enhance the drive's fault-tolerant capability. The mathematical model of this current is first established to provide a theoretical basis and a comprehensive understanding of the presented sensorless FOC. By virtue of this model, a second-order generalized integrator with a frequency-locked loop can be used as a simple and elegant way to extract position/speed estimates. Experimental results are provided to validate the proposed sensorless FOC philosophy.

Aiming at the problem that the traditional doubly salient electromagnetic machine (DSEM) cannot work when the excitation loss occurs, this article designs and analyzes a fault-tolerant DSEM for excitation loss, and the torque ripple suppression strategy under the fault-tolerant operation is studied. First, the characteristics of the output torque of DSEM before and after excitation-loss is analyzed, and a DSEM with a novel winding configuration is proposed to improve the fault tolerance. Second, under normal/excitation-loss conditions, the structure parameters of the fault-tolerant DSEM are analyzed to reveal the influence of the motor structure on its performance. Then, the steady-state torque of the fault-tolerant DSEM is compared with the traditional DSEM and the switched reluctance motor with the same size, which proves the effectiveness of the fault-tolerant design. By analyzing the inductance and torque characteristics, a torque ripple suppression strategy is proposed for the fault-tolerant DSEM without increasing the complexity of the system. Finally, a prototype is developed, and the experimental results verify the fault-tolerant capability of the prototype and the effectiveness of the proposed torque ripple suppression strategy. The research results of this article provide a specific implementation method for the fault-tolerant system design of DSEM under excitation loss.

This paper proposes a reconfigured topology of five-leg inverter for the open-end winding permanent magnet synchronous machine (OW-PMSM) driving system after the device fault condition. Due to the asymmetric structure and common DC bus of the reconfigured fault-tolerant five-leg inverter, the zerosequence current generated by the dead-time effect and inherent 3rd harmonic voltage of the open-end winding will deteriorate the output torque and the efficiency of the driving system. Thus, the asymmetric property and dead-time effect of the five-leg inverter on the distortion currents of OW-PMSM are analyzed, and an integrated control method with the closed-loop of zero-sequence current and the compensation of dead-time effect and 3rd harmonic voltage is employed to suppress the distortion current for the low current THD of the OW-PMSM. The effectiveness and validity of the high-performance OW-PMSM driving system based on the five-leg inverter were verified by the simulation and experiment results.

Due to the battery voltage performance of the dual power supply open-winding permanent magnet synchronous motor (OW-PMSM) system in electric vehicles, the dc bus voltages of the dual power supply varies and the traditional direct torque control (DTC) method will not be suitable and may lead to obvious torque ripples. Thus, in this article, based on the analysis of the effect of voltage vector on torque variation, a bus voltage ratio is employed in the switching table optimization strategy of DTC for OW-PMSM, the voltage vector selection method is also modified according to different voltage ratio, and then, the optimized control scheme for OW-PMSM over a wide bus voltage ratio is achieved to diminish the torque ripples. Finally, simulation models of the proposed method are built to verify the theory, and the corresponding experiments are also conducted to verify the feasibility and effectiveness of the proposed optimized control strategy.