Disturbance-observer-based control (DOBC) and related methods have been researched and applied in various industrial sectors in the last four decades. This survey, at first time, gives a systematic and comprehensive tutorial and summary on the existing disturbance/uncertainty estimation and attenuation techniques, most notably, DOBC, active disturbance rejection control, disturbance accommodation control, and composite hierarchical antidisturbance control. In all of these methods, disturbance and uncertainty are, in general, lumped together, and an observation mechanism is employed to estimate the total disturbance. This paper first reviews a number of widely used linear and nonlinear disturbance/uncertainty estimation techniques and then discusses and compares various compensation techniques and the procedures of integrating disturbance/uncertainty compensation with a (predesigned) linear/nonlinear controller. It also provides concise tutorials of the main methods in this area with clear descriptions of their features. The application of this group of methods in various industrial sections is reviewed, with emphasis on the commercialization of some algorithms. The survey is ended with the discussion of future directions.

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Disturbance-Observer-Based Control and Related Methods—An Overview

Solid-state switch-mode rectification converters have reached a matured level for improving power quality in terms of power-factor correction (PFC), reduced total harmonic distortion at input AC mains and precisely regulated DC output in buck, boost, buck-boost and multilevel modes with unidirectional and bidirectional power flow. This paper deals with a comprehensive review of improved power quality converters (IPQCs) configurations, control approaches, design features, selection of components, other related considerations, and their suitability and selection for specific applications. It is targeted to provide a wide spectrum on the status of IPQC technology to researchers, designers and application engineers working on switched-mode AC-DC converters. A classified list of more than 450 research publications on the state of art of IPQC is also given for a quick reference.

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A review of single-phase improved power quality AC-DC converters

This paper presents a review of recently used direct torque and flux control (DTC) techniques for voltage inverter-fed induction and permanent-magnet synchronous motors. A variety of techniques, different in concept, are described as follows: switching-table-based hysteresis DTC, direct self control, constant-switching-frequency DTC with space-vector modulation (DTC-SVM). Also, trends in the DTC-SVM techniques based on neuro-fuzzy logic controllers are presented. Some oscillograms that illustrate properties of the presented techniques are shown.

Direct torque control of PWM inverter-fed AC motors - a survey

Field-oriented control and direct torque control are becoming the industrial standards for induction motors torque control. This paper is aimed at giving a contribution for a detailed comparison between the two control techniques, emphasizing advantages and disadvantages. The performance of the two control schemes is evaluated in terms of torque and current ripple, and transient response to step variations of the torque command. The analysis has been carried out on the basis of the results obtained by numerical simulations, where secondary effects introduced by hardware implementation are not present.

FOC and DTC: two viable schemes for induction motors torque control

Unlike traditional passive harmonic filters, modern active harmonic filters have the following multiple functions: harmonic filtering, damping,isolation and termination, reactive-power control for power factor correction and voltage regulation, load balancing, voltage-flicker reduction, and/or their combinations. Significant cost reductions in both power semiconductor devices and signal processing devices have inspired manufactures to put active filters on the market. This paper deals with general pure active filters for power conditioning, and specific hybrid active filters for harmonic filtering of three-phase diode rectifiers.

Active Harmonic Filters

A novel direct torque control method for an induction motor is presented which is quite different from field-oriented control. Improving the torque response of a large-capacity induction motor using two sets of three-phase inverters and an open-data induction motor is of special concern. Instantaneous voltage vectors applied by an inverter have redundancy characteristics which provide some flexibility for selecting the inverter switching modes. By using this switching freedom, control is achieved according to the following priorities: (1) high-speed torque control; (2) regulation of the primary flux; (3) decreasing the zero phase sequence current; and (4) minimization of the inverter switching frequency. Simulations and experiments have been carried out to verify the feasibility of this priority control, accompanied by comparisons with another control scheme. Torque frequency-response corner frequencies above 2000 Hz have been experimentally measured, and time constants of 4 ms have been achieved for rotor-speed step responses from -500 to 500 r/min. The peak transient torque during the step change is about 20 times the rate torque. >

High-performance direct torque control of an induction motor

The authors describe a surface-mounted PM (permanent magnet) motor with the ratings of 5 kW and 180000 RPM for super-high-speed drive applications such as machine tools. A much larger air gap, compared with that of the existing PM motors, is used to reduce the slot ripples and hence the resultant eddy current loss in the metallic sleeve that retains the permanent magnets; otherwise, this loss would be objectionable at such high speeds. The motor is supplied from a quasi-current source inverter with the DC current controlled by a chopper and operated at a near-unity power factor by the use of a simple position sensorless control, to improve the motor efficiency. Analytic results are presented showing the slot ripple reducing effect of increasing the air gap length. To investigate the losses of the sleeve, several motors with different sleeves were manufactured and tested. Typical experimental results on these prototypes are given, which show that a motor efficiency of higher than 90% can be realized at the rated torque over a wide speed range. >

A super high speed PM motor drive system by a quasi-current source inverter

A new control method for magnetic levitation vehicles using linear induction motors is described. They can generate both thrust and attractive force. Selecting the voltage vectors of pulse-width-modulation (PWM) inverters appropriately allows decoupling control between the thrust and attractive force to be achieved. A module is constructed by four linear induction motors. The levitation control can be accomplished by detecting the gap length and controlling the attractive force of each linear induction motor. Ultrasonic wave sensors can stop the vehicle at any desired position using modified sliding mode control. Decoupling control between the thrust and attractive force was experimentally proved by means of a small model. The fluctuation of the gap length for the step change of the thrust is less than 0.1 mm. It would be suitable for relatively low-speed vehicles, such as an urban transit system. >

Decoupling control of thrust and attractive force of a LIM using a space vector control inverter

This paper presents a novel, simple method to enlarge switching frequency in the direct torque-controlled inverter for an induction motor drive, which makes an acoustically silent motor operation possible. It is actually impossible to raise the inverter switching frequency in the conventional system, although the hysteresis bandwidths for the stator flux and torque control are sufficiently diminished, because of the delay in estimating the flux and the torque. In order to overcome the problem, the proposed method introduces a dithering technique into the conventional system by superposing triangular waves with high frequency and minute amplitude on the flux error and the torque error, respectively. According to the simulation and experimental results, the stator flux ripple and the torque ripple were suppressed to approximately 30% compared with those of the conventional system. Also, the acoustic noise level of the motor was reduced to less than 56 dB over the whole speed range from 100 to 1500 r/min.

Enlarging switching frequency in direct torque-controlled inverter by means of dithering

This paper proposes a new initial rotor position estimation method of a sensorless permanent magnet (PM) synchronous motor at starting condition, which has no sensitivity to the armature resistance. The method is based on saliency of the rotor and employs the alternating magnetic field which is excited by a current controller. The phase differences between the magnetizing current references and the voltage references make it possible to estimate the rotor direction accurately without motor parameters, except the ratio of direct axis and quadrature axis inductance. Also, the magnetic pole is evidently identified by detecting the voltage reference oscillation phenomena caused by magnetic saturation, which can be performed without motor parameters. The experimental result has proven that the estimation error was within -4.5 to +2.5 mechanical degrees, even though the armature resistance varied to 125% of the nominal value.

Isao Takahashi

Papers

High-performance direct torque control of an induction motor

A super high speed PM motor drive system by a quasi-current source inverter

Decoupling control of thrust and attractive force of a LIM using a space vector control inverter

Enlarging switching frequency in direct torque-controlled inverter by means of dithering

Initial rotor position estimation method of sensorless PM synchronous motor with no sensitivity to armature resistance