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

In this paper, a novel dead time compensation method is presented that produces inverter output voltages equal to reference voltages. An experimental result is also presented to demonstrate the validity of the proposed method. It shows that the compensation of the dead time is possible up to a sub-microsecond range. Also, the reference voltage can be used as a feedback value, which is essential for sensorless vector control and flux estimation. The method is based on space vector pulsewidth modulation (PWM) strategy and it can be carried out automatically by an inverter controller for initial setup without any extra hardware.

Inverter output voltage synthesis using novel dead time compensation

A new on-line dead-time compensation technique for low-cost open-loop pulsewidth modulation voltage-source inverter (PWM-VSI) drives is presented. Because of the growing numbers of open-loop drives operating in the low-speed region, the synthesis of accurate output voltages has become an important issue where low-cost implementation plays an important role. The so-called average dead-time compensation techniques rely on two basic parameters to compensate for this effect: the magnitude of the volt seconds lost during each PWM cycle and the direction of the current. In a low-cost implementation, it is impractical to attempt an on-line measurement of the volt-seconds error introduced in each cycle-instead an off-line measurement is favored. On the other hand, the detection of the current direction must be done on line. This becomes increasingly difficult at lower frequencies and around the zero crossings, leading to erroneous compensation and voltage distortion. This paper presents a simple and cost-effective solution to this problem by using an instantaneous back calculation of the phase angle of the current. Given the closed-loop characteristic of the back calculation, the zero crossing of the current is accurately obtained, thus allowing for a better dead-time compensation. Experimental results validating the proposed method are presented.

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On-line dead-time compensation technique for open-loop PWM-VSI drives

This paper deals with an analysis of the vector-controlled induction-motor (IM) drive with a novel model reference adaptive system (MRAS)-type rotor speed estimator. A stability-analysis method of this novel MRAS estimator is shown. The influence of equivalent-circuit parameter changes of the IM on the pole placement of the estimator transfer function and the stability of the whole drive system are analyzed and tested. The influence of the adaptation-algorithm coefficients of the MRAS-estimator scheme is also tested. The allowable range of motor-parameter changes is determined, which guarantees the stable operation of the sensorless field-oriented IM drive with this speed and flux estimator. Dynamical performances of the vector-control system with the current-type MRAS estimator are tested in a laboratory setup.

Stator-Current-Based MRAS Estimator for a Wide Range Speed-Sensorless Induction-Motor Drive

This paper describes a new control algorithm which can enhance the dynamics of a sensorless control system and gives a precise sensorless control performance. Instead of the conventional sinusoidal-type voltage injection, a square-wave-type voltage injection incorporated with the associated signal processing method is proposed in this paper. As a result, the error signal can be calculated without low-pass filters and time delays, and the position estimation performance can be enhanced. Using the proposed method, the performance of the sensorless control can be enhanced; the bandwidth of the current controller was enhanced up to 250 Hz, and that of the speed controller was up to 50 Hz.

High-Bandwidth Sensorless Algorithm for AC Machines Based on Square-Wave-Type Voltage Injection

A new speed measurement system, which is suitable for microprocessor-based motor drive, and its application to speed regulator are explained.

A Microprocessor-Controlled High-Accuracy Wide-Range Speed Regulator for Motor Drives

A dead-time compensation method in vector-controlled pulse width modulator (PWM) voltage source inverters (VSIs) is proposed. The method is based on a feedforward approach that produces compensating signals obtained from the I/sub d/-I/sub q/ current and inverter output angular frequency references in the rotating reference (d-q) frame. It provides excellent inverter output voltage distortion correction for both fundamental and harmonic components. The correction is not affected by the magnitude of the inverter output voltage or current distortions. Since this dead-time compensation method allows current loop calculations in the d-q frame at a slower sampling rate, with a conventional microprocessor than calculations in the stationary reference frame, a fully digital. vector-controlled speed regulator with just a component current control loop is realized for PWM VSIs. Simulations and test results obtained for the compensation method are also described. >

Fully digital, vector-controlled PWM VSI-fed AC drives with an inverter dead-time compensation strategy

A method for estimating instantaneous speed, suited for a microprocessor-based speed regulator for motor drives, and the characteristics of the speed control system are described. Features of the proposed method include the estimation of instantaneous speed at a real-time point using values of average speed detected by counting for a certain time the output pulses of an encoder as well as the estimated value as the speed feedback signal for the speed regulator. Since this method allows compensation to be made for the lag time of the feedback signal caused by detection of the mean value, it contributes to improved stability of the speed regulator. In particular, this provides a significant suppression of the vibrations that are generated in motor-driven machinery. >

A microprocessor-controlled speed regulator with instantaneous speed estimation for motor drives

A new control method is described in which a microprocessor is used to regulate the speed of a dc motor driven by antiparallel-connected three-phase dual thyristor converters. A distinct feature of this speed regulating system is that speed response is improved by using a fast-response current controller for the internal loop. A fast-response current controller is obtained by employing a nonlinear compensation subloop and a proportional plus integral compensation subloop. The nonlinear compensation subloop is used to linearize the nonlinear load characteristics of the thyristor converter, which are encountered under discontinuous conduction states of current. The proportional plus integral compensation subloop reduces the deviation of detected current from the current reference. With these two current-control subloops a fast motor speed response is achieved under discontinuous as well as continuous conduction states; hence the steady-state accuracy of speed is improved. A speed regulator using a microprocessor was trial manufactured and tested with a 20-kW dc motor. It was found that an extremely fast controlled current response can be obtained even with a relatively long sampling period. Further, normal action was confirmed in four-quadrant operation.

A Microprocessor-Controlled Fast-Response Speed Regulator with Dual Mode Current Loop for DCM Drives

A multiple PWM GTO line-side converter with low switching frequency has been developed for industrial uses needing both higher capacity and higher performance. The multiple converter is composed of two GTO converter units connected in parallel through an interphase reactor. The switching frequency of the GTO thyristors in the multiple converter can be reduced to a quarter of that in the single converter. It is verified by simulations and experiments with a 2750 kVA GTO converter and inverter system with a 500 Hz switching frequency that the system has: (1) a unity power factor, (2) reduced harmonics, (3) bidirectional power flow, and (4) speed regulatory performance equal to that of an advanced cycloconverter drive system. Analogies between inverter control and converter control are also studied for the development of the converter control. >

Kenzo Kamiyama

Papers

A Microprocessor-Controlled High-Accuracy Wide-Range Speed Regulator for Motor Drives

Fully digital, vector-controlled PWM VSI-fed AC drives with an inverter dead-time compensation strategy

A microprocessor-controlled speed regulator with instantaneous speed estimation for motor drives

A Microprocessor-Controlled Fast-Response Speed Regulator with Dual Mode Current Loop for DCM Drives

A multiple PWM GTO line-side converter for unity power factor and reduced harmonics