Mohamad Koteich

Discussion on “AC Drive Observability Analysis”

In the paper by Vaclavek et al. ( IEEE Trans. Ind. Electron., vol. 60, no. 8, pp. 3047-3059, Aug. 2013), the local observability of both induction machine and permanent-magnet synchronous machine (PMSM) under motion-sensorless operation is studied. In this letter, the “slowly varying” speed assumption is discussed, and the PMSM observability condition at standstill is revisited.

Observability analysis of sensorless synchronous machine drives

This paper studies the local observability of synchronous machines using a unified approach. Recently, motion sensorless control of electrical drives has gained high interest. The main challenge for such a technology is the poor performance in some operation conditions. One interesting theory that helps understanding the origin of this problem is the observability analysis of nonlinear systems. In this paper, the observability of the wound-rotor synchronous machine is studied. The results are extended to other synchronous machines, adopting a unified analysis. Furthermore, a high-frequency injection-based technique is proposed to enhance the sensorless operation of the wound-rotor synchronous machine at standstill.

Energy equalization module for modular multilevel converters in variable speed motor drives

Modular Multilevel Converters (MMC) processing phase quantities at low frequency are vulnerable to high cell voltage ripples. MMC upper and lower arms processes pulsating power at fundamental and second harmonic phase components. As a consequence, arms are expected to buffer the energy difference exchanged between DC-link and each AC-phase. This buffered energy is translated into increased cell voltage ripple when operating at low phase frequency. Several remedies have been presented in literature, which can be classified under software and hardware methods. To address this short-come we introduced a plug-in hardware alternative that permit energy exchange between cells from upper and lower arms thus remarkably reducing capacitor voltage ripples caused by out of phase energy variations. The proposed method can improve MMC performance over the full operation region and is mainly attractive to low frequency operation such as in variable-speed motor drives where higher-than-nominal torques might be required for a wide speed range. Performed simulations over a synchronous machine using maximum torque per current control technique, conforms well with the analytical findings and shows the effectiveness of the proposed method.

Permanent magnet synchronous drives observability analysis for motion-sensorless control

Motion-sensorless control techniques of electrical drives are attracting more attention in different industries. The local observability of sensorless permanent magnet synchronous drives is studied in this paper. A special interest is given to the standstill operation condition, where sensorless drives suffer of poor performance. Both, salient and non-salient machines are considered. The results are illustrated using numerical simulations.

Discussion on “A Differential Algebraic Estimator for Sensorless Permanent-Magnet Synchronous Machine Drive”

Diao et al. are to be commended for proposing a new approach for permanent magnet synchronous machine (PMSM) position estimation, using the differential algebraic theory. In the following comments, we would like to highlight some points concerning the machine observability under the applied approach. In paper by Diao et al., it is claimed that the rotor position observability of the nonsalient PMSM is ensured regardless the speed, based on the relationship.

A unified model for low-cost high-performance AC drives: The Equivalent Flux concept

This paper presents a unified modeling approach of alternating current (AC) machines for low-cost high-performance drives. The Equivalent Flux concept is introduced. Using this concept, all AC machines can be seen as a non-salient synchronous machine with modified (equivalent) rotor flux. Therefore, complex salient-rotor machines models are simplified, and unified shaft-sensorless AC drives can be sought. For this purpose, a unified observer-based structure for rotor-flux position and speed estimation is proposed. The equivalent flux concept generalizes the existing concepts, such as the extended back-electromotive force, the fictitious flux and the active flux.

Flux estimation algorithms for electric drives: A comparative study

This paper reviews the stator flux estimation algorithms applied to the alternating current motor drives. The so-called voltage model estimation, which consists of integrating the back-electromotive force signal, is addressed. However, in practice, the pure integration is prone to drift problems due to noises, measurement error, stator resistance uncertainty and unknown initial conditions. This limitation becomes more restrictive at low speed operation. Several solutions, reported in the literature, are reviewed and compared. Emphasis is placed on the low-pass filter based algorithms that show good performance in steady-state as well as in transient operating conditions.

Local weak observability conditions of sensorless AC drives

Alternating current (AC) electrical drive control without mechanical sensors is an active research topic. This paper studies the observability of both induction machine and synchronous machine sensorless drives. Observer-based sensorless techniques are known for their deteriorated performance in some operating conditions. An observability analysis of the machines helps understanding (and improving) the observers behavior in the aforementioned conditions.

Self-sensing control of the externally-excited synchronous machine for electric vehicle traction application

This paper studies the possibility of removing the position sensor from electric vehicles (EVs) powertrains that employ the externally-excited synchronous machine (EESM) for traction. Three position estimation approaches are studied: back-electromotive-force integration, state-observer and high-frequency voltage injection approaches. Theoretical background is presented, a comparative performance analysis is performed, and experimental results on a 65-kW EESM drive test bench are shown. Some requirements for EV powertrains are emphasized.