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Single-phase dc-excited flux-switching machine (DCFSM) exhibits low manufacturing cost and rugged structure. This type of machine has better efficiency and torque density than single-phase induction machine and universal machine. In addition, single-phase DCFSM can generate lower torque ripple than other types of single-phase machines, e.g. switch reluctance machine and brushless DC machine. These advantages make it suitable for low-cost variable speed applications. However, single-phase DCFSMs requires accurate position feedback from a position sensor to generate smooth torque. The position sensor such as an encoder is not permitted in the low-cost applications due to its high cost. To eliminate the position sensor, this paper presents a novel sensorless control scheme for single-phase DCFSMs. Rotor position is estimated with the position-dependent armature current ripple induced by injecting high-frequency square-wave voltage to the field winding at standstill and low speeds. At medium and high speeds, armature mutual flux linkage is calculated and used to estimate the rotor position. A seamless transition between these two methods is achieve by mixing the calculated position error signals as the input for a single position estimator. The experimental results show that with the proposed scheme, the single-phase DCFSM can accelerate from standstill to the rated speed with 50% load, and to the maximum speed with 25% load, respectively.INDEX TERMS DC-excited flux switching machine; single-phase machine; sensorless control; flux linkage estimation; high-frequency voltage injection.

Safely starting a spinning position sensorless controlled permanent magnet synchronous machine is difficult because the current controller does not include information regarding the motor position and speed for suppressing the back-electromotive force (EMF)-induced current. This paper presents a restarting strategy for back-EMF-based sensorless drives. In the proposed strategy, the existing back-EMF and position estimator are used and no additional algorithm or specific voltage vector injection is required. During the restarting period, the current controller is set to a particular state so that the back-EMF estimator can rapidly estimate motor voltage without using rotor position and speed. Then, this voltage is used to decouple the back-EMF of the motor in the current controller in order to suppress the induced current. After the back-EMF is decoupled from the current controller, sensorless control can be restored with the estimated position and speed. The experimental results indicated that the induced current can be suppressed within four to five sampling periods regardless of the spinning conditions. Because of the considerably short time delay, the motor drive can restart safely from various speeds and positions without causing overcurrent fault.

High bandwidths and accurate current controls are essential in high-performance permanent magnet synchronous (PMSM) servo drives. Compared with conventional proportional–integral control, deadbeat current control can considerably enhance the current control loop bandwidth. However, because the deadbeat current control performance is strongly affected by the variations in the electrical parameters, tuning the controller gains to achieve a satisfactory current response is crucial. Because of the prompt current response provided by the deadbeat controller, the gains must be tuned within a few control periods. Therefore, a fast online current loop tuning scheme is proposed in this paper. This scheme can accurately identify the controller gain in one current control period because the scheme is directly derived from the discrete-time motor model. Subsequently, the current loop is tuned by updating the deadbeat controller with the identified gains within eight current control periods or a speed control period. The experimental results prove that in the proposed scheme, the motor current can simultaneously have a critical-damped response equal to its reference in two current control periods. Furthermore, satisfactory current response is persistently guaranteed because of an accurate and short time delay required for the current loop tuning.