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The flux observer method is widely utilized as a sensorless control technique in which the stator or rotor flux of IPMSM can be measured with a closed-loop observer or an integrator. However, DC-offset (DCoff), the ramp signal, and harmonics are consistently present in the acquired rotor flux because of an unidentified starting value, errors in the integral computation's current detection, and the inverter's nonlinearity. The aforementioned interference signals will drastically reduce the sensorless control efficacy. This work introduces an enhanced flux estimator with a negative feedback loop and PI controller to overcome the DC drift problem resulting from a pure integrator and a low-pass filter. Moreover, an optimal design approach of flux estimator structures with a broad range of speeds for Interior permanent magnet synchronous motor (IPMSM) drives is proposed, which utilizes an integrated topology of the voltage and current models incorporating a DC-offset PI-correction loop, actual and estimated flux magnitude's correction error. The flux vector's initial inaccuracy is eliminated, together with the DCoff and drift in the acquisition channel. A phase-locked-loop state estimator is utilized to derive the speed and position from the actual and estimated flux. The effectiveness and superiority of the suggested approach were proven by simulation and experimental findings for the IPMSM drives, which displayed high dynamic performances over varying scenarios. This reliable approach, including sensorless control, is suitable for all AC motors with sinusoidal flux distributions over a wide speed range. [ABSTRACT FROM AUTHOR]

The high-performance vector control technology of permanent magnet synchronous machines (PMSMs) relies on high-precision rotor position. The Hall-effect sensor has the advantages of low cost, simple installation, and strong anti-interference ability. However, it can only provide six discrete rotor angles in an electrical cycle, which makes high-precision vector control of PMSMs difficult. Hence, to obtain the necessary rotor position of PMSMs, a rotor position fitting method combining the Hall signal and machine flux information is proposed. Firstly, the rotor position signal output by the Hall-effect sensors is used to calibrate and update the stator flux obtained under pure integration. Then, based on the corrected stator flux and its relationship with current and angle, the rotor position and speed are obtained. Experimental verification shows that the rotor position observer combining Hall signal and flux information can reduce the initial value bias and integral drift caused by traditional average speed method hysteresis and pure integration method calculation of flux and can quickly and accurately track and estimate the rotor position, achieving high-performance vector control of PMSMs. [ABSTRACT FROM AUTHOR]

This article proposes a modified flux observer for sensorless direct torque control (DTC) of the dual three-phase permanent-magnet synchronous motor. The proposed method can improve torque performance without a position sensor. The flux observer is proposed to obtain the stator fluxes and rotor fluxes. The stator fluxes can be utilized to calculate the amplitude of torque and flux for DTC system. Meanwhile, the position information can be detected from the rotor fluxes by using a normalized phase-locked loop. This new flux observer can overcome the disadvantages due to the dc bias, initial value, and harmonic components. The stability of the proposed observer is also analyzed in this article. In addition, a fault-tolerant DTC scheme for open-circuit fault is introduced. The performances of torque control and position estimation are evaluated under healthy, open-circuit fault, and fault-tolerant conditions. Simulation and experimental evaluation are carried out to confirm the effectiveness of the proposed sensorless DTC scheme. [ABSTRACT FROM AUTHOR]

This article proposes an online maximum torque-per-Ampere (MTPA) control of an interior permanent-magnet synchronous motor (IPMSM) based on the square-wave voltage signal injection. Because the proposed method does not rely on a position sensor, it is applicable to sensorless IPMSMs. The proposed algorithm consists of a dynamic inductance estimator, frequency-adaptive flux observer, and an MTPA tracking controller. The proposed inductance estimation utilizes the pulsating square-wave voltage injection, which can maximize the injection frequency, and the dynamic performance can be preserved during the signal injection. Through the online flux and inductance estimation, the magnetic saturation of the IPMSM and the temperature variation can be fully considered in the MTPA control. The conventional rotor position estimator is replaced with the MTPA tracking controller, which does not rely on offline commissioning parameters. The proposed algorithm can operate under both the torque control and speed control mode, and accurate torque control on MTPA curve can be achieved. The simulation and experimental results demonstrate that the proposed method accurately tracks the MTPA point up to 200% of the rated torque in the mid- and high-speed region. [ABSTRACT FROM AUTHOR]

This article analyzes the effect of discretization in the frequency-adaptive flux observer (FAO). Although FAO has structural simplicity and ease of implementation, the discrete-time FAO has phase and gain errors in fundamental flux estimation. As a result, the estimated flux might be erroneous, especially in the high-speed region. For accurate flux estimation, this article analyzes how the voltage synthesis in the pulsewidth-modulation affects the stator flux. Through the analysis, the backward Euler method is selected for the primitive stator flux estimation. To mitigate the FAO's discretization error, the proposed FAO utilizes the integrators constructed at the rotor reference frame (RRF). Since the discretization error comes from the approximation error of the continuous-time integrator at the operating frequency, the proposed FAO conducts the fundamental flux extraction at the RRF, where the operating frequency components are treated as a dc signal. Thanks to the coordinate transformation, the FAO can be discretized with no error while keeping the structure of double integrators. The proposed method is verified through the computer simulation and experimental test. [ABSTRACT FROM AUTHOR]

When the permanent magnet synchronous motor (PMSM) works in the high-speed region with low carrier ratios, the performance of the rotor flux observer has a great influence on the loading capacity and stability of the speed sensorless vector control system. The problem of the adaptive compensation flux observer (ACFO) of the PMSM at low carrier ratios is analyzed in this paper, and an ACFO with a feedback delay component is presented. After retuning the PI regulator parameters, the new expression related to carrier ratio is obtained, which can improve the performance of the flux observer at low carrier ratios and make the torque and current loop response faster. Meanwhile, the stability of different Euler approaches of the integrator for ACFO in the discrete domain is analyzed, and a new Euler with a coefficient is proposed to combine the merits of the backward Euler and the trapezoid Euler. It shows better performance at low carrier ratios. Finally, the effectiveness of the discrete ACFO is verified by experiments. [ABSTRACT FROM AUTHOR]

A new robust adaptive hybrid second-order generalized integrator (SOGI) based rotor flux observer (RFO) for self-sensing control of solar photovoltaic array fed permanent magnet synchronous motor drive for water pump is developed in this article. The conventional pure integrator based RFO introduces dc offset, saturation, and harmonics, whereas a low-pass filter based produces attenuation and phase delay. To overcome these problems, a new n-layer hybrid SOGI structure (HSS) is developed and its four-layer version is used in the system. An adaptive frequency tracker is then integrated with four-layer HSS to track wide variations in system frequency due to dynamic solar irradiations, which results in an adaptive hybrid SOGI (AHS) structure. However, the AHS is sensitive to system parametric uncertainties. Thus, the sliding mode approach is used to impart the robustness. This results in new robust AHS (RAHS) structure for accurate observation of rotor flux. The improved performance of developed RAHS over its conventional counterparts is proved through Bode curves and flux loci while test results validate its performance. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A speed estimation scheme based on the particle swarm optimization algorithm flux observer is proposed for a sensorless rotor field direct orientation controlled induction motor drive. The stator current and rotor flux was used to establish both the rotor field direct orientation controlled induction motor drive and the rotor-flux observer. The estimated synchronous angle position was acquired from a current-and-voltage parallel-model rotor estimator for implementation of the exact coordinate transformation to achieve a perfect rotor field direct orientation controlled induction motor drive. The rotor-flux observer was designed using the Lyapunov stability theory, and the estimated rotor speed was derived from the developed the rotor-flux estimator; this estimated speed was unaffected by the slip speed. The gain matrix of this flux observer was obtained using the particle swarm optimization algorithm because it is simple, achieves rapid convergence, and is suitable for a variety of conditions. This system was simulated using the MATLAB/Simulink® toolbox, and all the control algorithms were realized by a TI DSP 6713-and-F2812 control card. Both simulation and experimental results confirmed the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

Flux-linkage based sensorless control method is well-known and has been widely used in the control of electrical machines. The closed-loop flux observer (CLFO), which is the adaptive combination of the machine voltage and current models, is commonly adopted. It can cover a wide speed operation range and was considered to be able to solve the dc drift and initial value problem associated to the pure integrator used in the observer. However, it is reported in this paper that this popular CLFO cannot always work as expected. In some situations, dc-offsets cannot be removed by this flux observer, causing large system oscillation at fundamental frequency and is very harmful to the drive system. This important issue has not been reported and discussed in the existing literatures of the CLFO. In this paper, this phenomenon is experimentally illustrated and solution to damp this harmful oscillation is proposed and verified experimentally on a synchronous reluctance machine drive system. [ABSTRACT FROM AUTHOR]

For field-oriented control (FOC) of induction motors, accurate estimation of flux is important. Among the various flux estimation methods, the voltage model flux observer exhibits superior performance in situations where there is detuning of rotor parameters, such as rotor resistance and mutual inductance, because this model is robust to the detuning of these parameters. However, it is difficult to implement the voltage model, which includes pure integration, because of the dc saturation and dc drift problems. A number of methods have been developed to overcome this problem, including the Gopinath model flux observer, which can completely solve these problems. However, this model has a critical weakness in terms of parameter sensitivity in the mid-speed region because of the property of its characteristic function. In this paper, an analysis of parameter sensitivity of existing flux observers is discussed. A method for a voltage model flux observer design based on the Gopinath model is presented. Through an analysis of the characteristic function of the observer, the voltage model is designed. Finally, the operation of the proposed method is proven by simulations and experiments. [ABSTRACT FROM AUTHOR]

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 electromotive force (EMF) tracking method. [ABSTRACT FROM AUTHOR]

This paper introduces a novel flux observer for direct torque controlled interior permanent magnet brushless AC (IPM-BLAC) drives over a wide speed range including standstill. The observer takes machine nonlinearities into account and is independent of inverter nonlinearities, dead time, and armature resistance variation at steady states since such inaccuracies are compensated quickly by measured phase currents. Magnetic saturations in the stator and rotor cores, cross-coupling effects of flux linkages of the motor, and spatial harmonics in the magnetomotive force are all considered in the novel scheme. There is no filter; hence, no delays and oscillatory responses like in conventional schemes where filters are employed to prevent integrator drift issue. Superiority of the observer when compared to the state-of-the-art schemes has been illustrated by both extensive simulations and experimental results of a 10-kW IPM-BLAC machine designed for traction applications. [ABSTRACT FROM AUTHOR]

This paper presents a digital implementation of deadbeat–direct torque and flux control (DB-DTFC) for induction machines at low switching frequencies (SFs). For high SFs, existing discrete-time flux observers and Volt–second-based inverse torque models used for DB-DTFC achieve acceptable flux estimation accuracy and fast torque response. However, the flux estimate is less accurate when the SF is reduced and the DB-DTFC performance degrades. This paper develops a more suitable flux observer and Volt–second-based inverse torque model that minimizes flux estimation error and improves torque control for DB-DTFC. Simulation and experimental results are provided to evaluate the performance of the proposed observer and torque model at very low SFs. Consequently, digital implementation of low-SF DB-DTFC on high-power induction machines is feasible. [ABSTRACT FROM AUTHOR]

This paper proposes a Sensorless Field Oriented Control for surface mounted permanent magnet synchronous motor combining two approaches for different rotor speed ranges. The active flux observer is applied at low speed and combined with a back-EMF observer at high speed. This combination allows for an improvement of the rotor position estimation for a large speed range and is therefore resulting in a higher stability of the sensorless control scheme when compared to the conventional back EMF method. The presented approach is discussed based on simulations. [ABSTRACT FROM AUTHOR]

The high-speed operation region of interior permanent magnet (PM) (IPM) motor drives is investigated, with particular attention to the maximum-torque-per-voltage operation. A technique is proposed for the control of the drive in such region, based on direct-flux field-oriented vector control. The proposed control is easy to implement, does not require the accurate knowledge of the motor model, and showed to be robust toward the effects of iron losses, position estimation errors, and dc-link variations. Moreover, it is suitable for operation in the inverter overmodulation range. Experimental results are provided for a 600-W IPM drive for home appliances. [ABSTRACT FROM PUBLISHER]

An adaptive observer is proposed for concurrent estimation of rotor fluxes, unknown dc-link voltage, and rotor resistance of induction motor with voltage source inverters. For the reported flux observers and parameter estimators, the implied assumption had been that the input voltages were measured by sensors, or presumed to be known, for example while plug-in converters were utilized. However, this assumption may not be valid due to bus voltage variations, such as for battery powered servo drives, or propulsion system in hybrid electric vehicles. A drift in input voltage measurement results in state and parameter estimation errors. The proposed observer is capable of concurrent flux and dc-link voltage observation with online tuning of rotor resistance, while the phase currents and rotor speed are measured. No terminal voltage measurement is needed for this adaptive observer. The stability of the proposed observer is proved based on a Lyapunov function. Besides, it is shown that injection of a diagnosis signal is necessary to force the estimated parameters converge to the right values regardless of their initial conditions. A complex programmable logic device is implemented for the experimental setup, which controls an intelligent power module including insulated gate bipolar transistors. Extensive simulation and experimental tests verify the asymptotic convergence of the proposed observer. [ABSTRACT FROM AUTHOR]

This paper proposes a novel Lyapunov-based adaptive observer to estimate internal states, or fluxes, core loss, and rotor resistance of induction motor simultaneously. Traditionally, flux observers for induction motors are employed by some control algorithms, loss optimization strategies, and also torque estimators. Nevertheless, stator core loss has been generally neglected in the flux observer equations. In this paper based on the induction motor model including stator core loss resistance, a flux observer is derived. The proposed observer is capable of concurrent flux and core loss observation with online tuning of rotor resistance, while the phase currents and rotor speed are measured. The stability of the proposed observer is proved based on a Lyapunov function. Then, based on a circuit based analysis, a condition for asymptotic convergence of the estimated parameters is discussed. Experimental tests verify the validity of the proposed adaptive observer. [ABSTRACT FROM AUTHOR]

Properly formed discrete-time recursive models of a stator and rotor flux-linkage observer are presented. A model delay in the flux-linkage observer, which hindered previous work, is identified. To remove this delay, a new stationary frame current observer is developed and experimentally verified. With this new observer system, the flux linkages are properly estimated for the next sample instant, thus removing the computational delay. The improved and the delayed flux observer are evaluated in a deadbeat direct torque control algorithm. [ABSTRACT FROM AUTHOR]

Vector control of induction motors is widely used for industrial applications. On-line parameter identification and speed sensorless control are being studied actively. A representative method for these problems is the application of an adaptive full-order observer. The rotor flux for vector control is estimated by a full-order observer and machine parameters, or the rotor speed is determined by an adaptive algorithm. In this paper, a new vector control scheme with parameter identification is proposed. This method is based on the adaptive full-order observer. However, the observed currents which are usually estimated in the voltage model are considered as command currents and the voltage model is used for the current controller. As a result, the proposed system is simpler than the conventional adaptive full-order observer system. Since the proposed system is composed of an induction motor model in a synchronously rotating reference frame, the well-known slip frequency control block is contained. The arrangement of the poles which are related to the torque transfer function is discussed. A linear model is derived taking into account the effects of the change of the stator and rotor resistances. The trajectories of poles and zeros of the torque transfer function are computed and discussed for various system parameters. Identification of stator and rotor resistances is confirmed by simulation using a nonlinear system model. The proposed idea is applied to a speed sensorless system; this system has a similar configuration to those of existing systems under some assumptions. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 119(4): 66–76, 1997 [ABSTRACT FROM AUTHOR]