A model-reference adaptive system (MRAS) for the estimation of induction motor speed from measured terminal voltages and currents is described. The estimated speed is used as feedback in a vector control system, thus achieving moderate bandwidth speed control without the use of shaft-mounted transducers. This technique is less complex and more stable than previous MRAS tacholess drives. It has been implemented on a 30 hp laboratory drive, where its effectiveness has been verified. >

Adaptive speed identification for vector control of induction motors without rotational transducers

Controlled induction motor drives without mechanical speed sensors at the motor shaft have the attractions of low cost and high reliability. To replace the sensor the information on the rotor speed is extracted from measured stator voltages and currents at the motor terminals. Vector-controlled drives require estimating the magnitude and spatial orientation of the fundamental magnetic flux waves in the stator or in the rotor. Open-loop estimators or closed-loop observers are used for this purpose. They differ with respect to accuracy, robustness, and sensitivity against model parameter variations. Dynamic performance and steady-state speed accuracy in the low-speed range can be achieved by exploiting parasitic effects of the machine. The overview in this paper uses signal flow graphs of complex space vector quantities to provide an insightful description of the systems used in sensorless control of induction motors.

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Sensorless control of induction motor drives

A system for delivering radiofrequency energy to ablate tissue comprises a radiofrequency generator and an intravascular catheter. The catheter includes both a radiofrequency ablation electrode and a temperature sensor within its distal end. Delivery of power to the ablation electrode may then be controlled based on electrode temperature using a cascade control system wherein analog temperature controller adjusts the set point to a secondary power controller. Alternatively, power delivered to the patient can be controlled directly based on a power set point. A sinusoidal RF signal is provided to avoid energy attenuation and the sinusoidal RF signal may be pulsed to avoid buildup of coagulum on the catheter tip while providing high power to create large lesions. A verification circuit checks the continuity of circuits in the catheter.

Method and system for radiofrequency ablation of tissue

This paper describes a new approach to estimating induction motor speed from measured terminal voltages and currents for speed-sensorless vector control. The proposed approach is based on observing the instantaneous reactive power of the motor. The estimated speed is used as feedback in an indirect vector control system. The described technique is very simple and robust to variations of motor parameters. The new approach is not dependent upon the knowledge of the value of the stator resistance, nor is it affected by stator resistance thermal variations. Furthermore, pure integration of sensed variables, in principle, is not required at all. Therefore, this new method can achieve much wider bandwidth speed control than previous tacholess drives. The effectiveness is verified by simulation and experiment. >

Robust speed identification for speed sensorless vector control of induction motors

A system for delivering radiofrequency energy to ablate cardiac tissue comprises a radiofrequency generator and an intravascular catheter. The catheter includes both a radiofrequency ablation electrode and a temperature sensor within its distal end. Delivery of power to the ablation electrode may then be controlled based on electrode temperature using a cascade control system wherein analog temperature controller adjusts the set point to a secondary power controller. Alternatively, power delivered to the patient can be controlled directly based on a power set point. Reuse of the catheter is prevented by a fuse within the catheter which is sensed prier to power delivery and broken prior to disconnection of the catheter.

Method and system for radiofrequency ablation of cardiac tissue

The utilization of the squirrel cage induction motor as an autonomous induction generator is briefly reviewed. In view of potential new applications, the discussion focuses on a simple exciter scheme based on using a static reactive power generator implemented with fixed capacitors and thyristor controlled inductors. The feasibility of the proposed scheme with naturally commutated thyristors is verified by measurements on a test setup employing a standard 15-hp induction motor.

Static Exciters for Induction Generators

In certain types of adjustable frequency induction motor drives, optimal control of the motor can be best implemented by using information on the motor slip frequency. Unfortunately, this generally requires the use of an electromechanical speed transducer coupled to the shaft. The presence of this transducer spoils the general characteristics of ruggedness and mechanical simplicity typical of an ac drive. This paper discusses an improved method of obtaining the slip information without the use of rotary transducers of any kind. By sensing the electrical quantities applied to the motor (voltages, currents, and phases) and by performing simple signal processing operations on the sensed quantities, an analog signal proportional to the slip level is derived and used in motor control functions.

Variable Speed induction Motor Drives Use Electronic Slip Calculator Based on Motor Voltages and Currents

At least two active conditioners are connected in series with a common DC source, and are mounted as a unit between two pairs of AC terminals to act either as a tie-in link between two AC power sources, as a buck/boost regulator between one AC power source and its load, or as VAR compensator as well as active power conditioner between phases of a multiphase AC option.

Active power conditioner system

In order to maintain low telephone interference (IT factor) during its normal operation and to establish rapid-post-fault voltage support to preserve the integrity of electric power transmission lines in the presence of degraded system impedance and harmonic instability, amplitude detection in a transmission voltage regulator (static VAR generator, SVG) is provided based on real time conventional, or fast, Fourier analysis, data samples being used to establish the fundamental voltage amplitude and collected during a specific, frequency tracking sliding window that precedes the amplitude reading by one line voltage cycle of the transmission line. The number of samples in the window is an integer multiple of the line frequency and, in the case of conventional analysis, the pulse number of the switching power circuit is used in the SVG. The amplitude value is updated after each sampling by shifting (sliding) the one cycle sample data base in a first in - first out manner.

Transmission line voltage detector for static VAR generator

A static VAR generator circuit having a control system adapted to utilize the values of three phase load currents to generate time delayed firing angles for thyristor controlled inductors which are utilized with parallel capacitors to provide unity power factor and balanced electrical currents to the AC source. The time delayed firing angles are calculated from integrating furnace load currents over prescribed intervals during real time to thus maintain balanced load current at specified phase angles, usually zero, in the three phase system.

Michael B. Brennen

Papers

Static Exciters for Induction Generators

Variable Speed induction Motor Drives Use Electronic Slip Calculator Based on Motor Voltages and Currents

Active power conditioner system

Transmission line voltage detector for static VAR generator

Method and control apparatus for static VAR generator and compensator