New sensorless observers (i.e., from stator currents/voltages measurements), to be included into a simple observer-based sensorless control for the tracking of nondefinitely zero speed references in nonsalient-pole surface Permanent Magnet Synchronous Machines (PMSMs), are proposed. They are obtained, through a 'minimum distance' modification, from recently presented position-sensorless observers (i.e., from rotor speed and stator currents/voltages measurements). The rotor speed estimate is here directly provided by the Phase Locked Loop (PLL)-based third-order Steady-State Linear Kalman Filter (SSLKF) that has been previously used to mitigate the distortions on the estimated position. Experimental results illustrate the effectiveness of the proposed approach in a speed sensor fault-tolerant scenario.

The Current Source Inverter (CSI) is a power electronics topology that allows for the realization of variable speed drives (VSD). Compared to the most common Voltage Source Inverter (VSI), which can be directly connected to a voltage source, the CSI needs a pre-stage to generate a constant current bus. This paper therefore seeks to challenge this 'accepted' consideration that a CSI always needs this pre-circuit and seeks to remove this circuit by proposing an innovative i dc Current Control scheme. The proposed scheme is applied to a single stage motor drive driven by a CSI converter. It is shown how implementing this control scheme removes the need for the front-end stage, thus removing an unnecessary converter and optimizing the efficiency at the same time. The CSI state-space equations are presented and the developed models are verified using simulations. Stability analysis of small -signal model is considered through Nyquist criterion with the robustness in presence of variations of the most important system parameters. Experimental results driving a Permanent Magnet Synchronous Machine (PMSM) are shown confirming the validity of the proposed control, potentially paving the way to a larger adoption of the CSI topologies for motor drive applications.

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