Back Electromotive Force Estimation Research Articles

An SRF-PLL-Based Sensorless Vector Control Using the Predictive Deadbeat Algorithm for the Direct-Driven Permanent Magnet Synchronous Generator

This paper proposes an enhanced sensorless vector control strategy using the predictive deadbeat algorithm for a direct-driven permanent magnet synchronous generator (PMSG). To derive favorable sensorless control performances, an enhanced predictive deadbeat algorithm is proposed. First, the estimated back electromotive force (EMF), corrected by a cascade compensator, was put into a deadbeat controller in order to improve the system stability, while realize the null-error tracking of the stator current at the same time. Subsequently, an advance prediction of the stator current based on the Luenberger algorithm was used to compensate the one-step-delay caused by digital control. Maintaining the system stability, parameters of the controller were optimized based on discrete models in order to improve the dynamic responses and robustness against changes in generator parameters. In such cases, the proposed methodology of synchronous rotating frame phase lock loop (SRF-PLL), which applies the estimated back EMF, can observe the rotor position angle and speed without encoders, realizing the flux orientation and speed feedback regulation. Finally, the simulation and experimental results, based on a 10-kW PMSG-based direct-driven power generation system, are both shown to verify the effectiveness and feasibility of the proposed sensorless vector control strategy.

Inter-Turn Fault Detection in PM Synchronous Machines by Physics-Based Back Electromotive Force Estimation

In this paper, the inter-turn short circuit fault detection in permanent magnet synchronous machines (PMSM) using an open-loop physics-based back electromotive force (EMF) estimator is presented. The back EMF estimator is designed based upon a current mode tracking scheme. The thermal and saturation aspects of the machine are considered in the design of the estimator. The design procedure and stability criteria of the estimator are presented in detail. The fault detection is carried out based on the difference between the estimated back EMF and a reference back EMF. A 0.8 (kW) PMSM is studied experimentally as well as numerically under different inter-turn fault and operational contingencies. The numerical modeling is accomplished by a finite-element-based model coupled with the thermal network and polluted with inter-turn fault. The acceptable agreement between the simulated and experimental result validates the modeling process. The back EMF estimator fault detection system is led to discriminative inter-turn fault signatures in a fraction of second for wide speed range even in the presence of harmonic loads and dynamic eccentricities.

Modified sliding mode observer for wide speed range operation of brushless DC motor

This paper describes an adaptive gain sliding mode observer for brushless DC motor for large variations in speed. Sensorless brushless DC motor based on sliding mode observer exhibits multiple zero crossing in back electromotive force (EMF) which leads to commutation problems at low speed. In this paper, a modified sliding mode observer incorporating a speed component in the estimation of back EMF is proposed. It is found that after incorporating the speed component in the back EMF observer gain, multiple zero crossings at low speeds and phase shift at higher speeds are eliminated. The trapezoidal back EMF observer is implemented experimentally on a digital signal processor (DSP) board. The effectiveness of the proposed method is demonstrated through simulations and experiments.

Sensorless Control of Brushless DC Motors With Torque Constant Estimation for Home Appliances

A new sensorless control algorithm for brushless dc motors (BLDCMs) is proposed in this paper. The torque constant of a BLDCM is used as a reference signal for position detection because it is constant during the entire speed range and can be estimated by calculating the ratio of the back electromotive force (EMF) to the rotor speed. By using both a disturbance observer and the torque constant estimation error, the rotor speed can be obtained. The back EMF can be easily obtained from the voltage equation of the BLDCM. The estimated back EMF decreases simultaneously with the estimated torque constant at the commutation point. By using this phenomenon, the commutation of the phase currents can be done automatically at the drop point of the estimated torque constant. Unlike conventional back-EMF-based methods, the proposed method provides highly accurate sensorless operation even under low speeds because only the drop of the torque constant is used for position detection and current commutation. Therefore, the position accuracy is not affected by the electric parameter errors of the BLDCM. Also, this algorithm does not require an additional hardware circuit for position detection. The validity of the proposed algorithm is verified through several experiments.

ROBUST ESTIMATION OF MECHANICAL VARIABLES IN PERMANENT MAGNET SYNCHRONOUS MOTORS

This paper deals with rotor position and speed estimation of permanent magnet synchronous motors. A reduced order observer based on back electromotive force estimation is proposed for estimating mechanical variables. Robustness against model uncertainty is analyzed. Under exact model assumption the estimation error converges to zero in exponential way, while a residual estimation error appears in presence of uncertainties. For this reason, estimation error bounds are calculated when uncertainty in both the mechanical and the electrical submodels are taken into account. The observer performance is tested through simulations.

A source voltage-clamped resonant link inverter for a PMSM using a predictive current control technique

A simple source voltage-clamped resonant link (SVCRL) inverter is proposed to clamp the DC-link voltage to the input source voltage and reduce the current rating of a resonant inductor. The current control of a permanent magnet synchronous motor (PMSM) employing a predictive current control technique (PCCT) for the SVCRL, inverter is also investigated to overcome the disadvantage of the current-regulated delta modulation (CRDM) control technique. By employing the PCCT based on the discrete model of a PMSM and estimation of back electromotive force (EMF), the minimized current ripple with a small number of switchings can be obtained. Finally, the comparative computer simulation and experimental results are given to show the usefulness of the proposed technique.