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The operation of a brushless permanent-magnet machine requires rotor-position information, which is used to control the frequency and phase angle of the machine's winding currents. Sensorless techniques for estimating rotor position from measurements of voltage and current have been the subject of intensive research. This paper reviews the state of the art in these sensorless techniques, which are broadly classified into three types: motional electromotive force, inductance, and flux linkage. Index Terms--Brushless machines, estimation, permanent-magnet (PM) machines, position measurement, reviews.

This paper describes a modern solution to real-time rotor position estimation of brushless permanent magnet (PM) motor drives. The position estimation scheme, based on flux linkage and line-current estimation, is implemented in real time by using the abc reference frame, and it is tested dynamically. The position estimation model of the test motor, development of hardware, and basic operation of the digital signal processor (DSP) are discussed. The overall position estimation strategy is accomplished with a fast DSP (TMS320C30). The method is a shaft position sensorless method that is applicable to a wide range of excitation types in brushless PM motors without any restriction on the motor model and the current excitation. Both rectangular- and sinewave-excited brushless PM motor drives are examined, and the results are given to demonstrate the effectiveness of the method with dynamic loads in closed estimated position loop. Index Terms - Brushless permanent magnet motors, digital signal processors, rotor position sensorless operation.

This paper introduces a flywheel energy storage device capable of enhancing the fuel economy of a hybrid-type road vehicle. A number of possible drive types are considered and the permanent magnet machine drive is shown to provide the best solution. Reasons for selecting a device using an axial-field configuration with single-rotor and double-stator sections are described. Electrical, magnetic, and mechanical design data are presented for a full-scale prototype device with 240 kJ of usable energy storage and 25 kW of power transfer, operating at speeds up to 50 000 r/min, with a 10% duty cycle. Index Terms - Electric vehicles, energy storage, flywheels.

A rigorous method of applying observability criteria to the estimation of winding currents in brushless dc drives is presented. Observability is related to both the drive's operating condition, both motoring and regenerating, and to the PWM switching strategy being employed. The precise conditions under which motor winding currents can be estimated from measurements of de link current are clearly defined. A modified single current sensor arrangement, in which switching device currents are measured, is shown to improve the observability of currents with complementary switching, but to have an adverse effect on observability with the basic switching strategy. An arrangement involving two current sensors allows discontinuous estimation of the winding currents for all operating conditions and both switching strategies. The primary advantage of this technique is that measurements by each sensor are made equally on all three phases of the motor.

In classical direct torque control (DTC), an inverter switching event can occur once in each control update period. Because the nature of the inverter switching event is unconstrained, it is essential to limit the inverter switching frequency, and hence the control update period, to ensure that under no circumstances is the allowable switching frequency of any individual power device exceeded. Consequently the switching capability of individual power devices is generally under-utilized, and the control scheme produces high levels of ripple in the motor current and torque. This paper describes a new strategy for device switching and voltage vector selection in DTC. The basis of the strategy is an increase in the control update frequency, while limiting the switching rate of each inverter leg. Although the rate at which device switching events may occur is unchanged, the higher control update frequency leads to higher resolution timing of switching events. The advantages of the strategy, demonstrated by experimental results on a 3 kW induction motor drive, are a significant reduction in the steady-state torque ripple as well as a faster transient response. Index Terms--Induction motor drives, power electronics, real-time systems, switching functions, torque control.

This paper describes a new algorithm for the estimation of rotor position in a switched reluctance motor. It is based on a recursive least-squares estimator deducing both position and speed. A particular advantage of the algorithm is its ability to extract information about rotor position at very low speeds (one electrical cycle per minute) from voltage and current waveforms sampled only at the converter switching frequency. Experimental results for a 12/8 motor demonstrate that estimation is possible over the full range of operating conditions, including the field-weakening region, with a typical accuracy of better than two mechanical degrees. The paper also illustrates the performance of the algorithm by showing it operating within a sensorless position controller. Index Terms--Estimation, least-squares methods, position measurement, reluctance motor drives.

Tuning of electric drive speed controllers is complicated by nonlinearities. Usual practice obtains controller settings with conventional linear analysis methods and then tunes the settings using trial-and-error methods during commissioning. An alternative approach, using genetic algorithms for the online tuning, is proved experimentally to optimize the drive's response efficiently. These settings are critically dependent on operating point. Index Terms--Electric drives, genetic algorithms, speed control, tuning.