flux observer

This paper introduces an enhanced speed self-sensing method that tracks the stator flux linkage in induction machines at very low speeds. Volt-second sensing technology is used to mitigate the inverter nonlinearity, which is the major source of flux estimation error in the very-low-speed range. By integrating volt-second sensing in the Gopinath style closed-loop flux observer, the rotor speed information with more precision and lower noise is extracted from the estimated stator flux. Experimental results show that the proposed self-sensing method extends the low speed operating range, reduces the speed and torque ripple, and increases the disturbance rejection capability compared with the traditional self-sensing method based on the voltage integration method and the back-EMF tracking method.

High power applications with low switching frequencies as well as high speed applications with high fundamental frequencies operate at a low switching-to-fundamental (S2F) frequency ratio.  With a low S2F frequency ratio, it is challenging to achieve high torque control accuracy and dynamic performance. This paper identifies control issues that yield performance degradation at a low S2F frequency ratios, for traditional field oriented control (FOC) and for deadbeat-direct torque and flux control (DB-DTFC) induction machine drives. It is documented that by eliminating synchronous reference frame current regulation, DB-DTFC demonstrates advantages to achieve a more desirable torque control performance in low-S2F-ratio applications. Three progressively more accurate DB-DTFC torque models are compared in terms of torque control accuracy and computation time to FOC and standard high switching frequency DB-DTFC. A general guideline is proposed to select the most suitable model for DB-DTFC drives at an arbitrary S2F ratio for high power or high speed applications.

Bu çalışmada, asenkron motor için uyarlamalı akı gözlemleyici tabanlı hız algılayıcısız doğrudan moment kontrolü gerçekleştirilmiştir. Asenkron motor durağan referans düzleminde ortaya koyulmuş, sabit hız ve değişken hız referans değerleri için sistem davranışı gözlemlenmiştir.

Flux weakening techniques have been developed for field oriented control (FOC) drives to achieve the maximum torque capability above the base speed. Deadbeat-direct torque and flux control (DB-DTFC) has the advantages of precise torque and flux control and reduced parameter sensitivity compared to FOC, thus it has the benefit of more consistently achieving the maximum torque capability in the flux weakening region more accurately. This paper introduces a flux weakening strategy for DB-DTFC. Considering voltage and current limits, a simple solution to the optimal trajectory for the stator flux magnitude is derived to achieve the maximum feasible torque over the entire operating range. Results show that the speed control is extended to a significantly higher range beyond the base speed. Torque control is less sensitive to machine parameters and has better dynamics in the flux weakening region compared with the traditional FOC drives. Self-sensing is also investigated in the flux weakening region. Challenges of self-sensing are addressed to significantly extend the high-speed operating range.