Modern pulsewidth modulation (PWM) inverter motor drives are affected by dangerous common-mode currents due to the high rate of variation of the modulated voltage. An inexpensive alternative to low-pass filters, which are normally used to limit common-mode currents, consists in reducing such currents by using suitable modulation strategies. In this paper, a new approach for designing PWM strategies is presented, which is able to reduce common-mode currents by limiting the amount of variations of the common-mode voltage. The main characteristics of the proposed approach are experimentally evaluated on a standard PWM induction motor drive.

This paper analyzes different aspects of the maximum-torque-per-ampere (MTPA) vector control of interior permanent-magnet synchronous motors at steady state and transient. Two different implementations are considered: a nonlinear-model-based MTPA profile including saturation and cross-saturation effects and a technique based on the maximization of the motor input power versus stator current. Furthermore, this paper analyzes the torque evolution during a transient under an MTPA control strategy on motors with different characteristics. Useful modifications of the current loop are suggested to improve the drive performance. The effects of the torque transient on the sensorless rotor position estimation are also taken into consideration, in case a sensorless MTPA implementation is required. Experimental results confirm the theoretical analysis, showing the benefits of the new control schemes.

This paper presents a position sensorless vector control able to drive synchronous reluctance motors in any working condition, including low- and zero-speed operations. The proposed control scheme is based on calculating the rotor position from the measurement of an additional high-frequency stator current component and allows a low-cost implementation; moreover, it does not require the knowledge of any motor parameter, nor particular care for motor starting. Simulation and experimental results on a 1.5-kW prototype are presented to evaluate the consistency of the developed technique.

This paper presents a novel approach to estimate the instantaneous position of the air-gap flux in standard induction machines at low and zero speed. The proposed approach is based on the generation of a high-frequency rotating field that, interacting with the main field, generates a high-frequency zero-sequence flux component. By demodulating such a component, which is always present, irrespective of speed and load levels, it is possible to detect the air-gap flux position. The proposed method allows one to overcome some key drawbacks of sensorless approaches based on high-frequency voltage injection and, compared to previous sensorless schemes exploiting the third harmonic voltage, improves the accuracy and extends the operating area up to zero speed. Experimental tests are shown in order to practically confirm the expected features of the proposed system.