Variable Speed Induction Motor Research Articles

Modeling of line side harmonic currents produced by variable speed induction motor drives

An analysis method to model and calculate the line side harmonic currents produced by variable speed induction motor drives is proposed. An accurate analytical investigation of the line currents in the presence of a power conversion system with a load represented by a PWM inverter feeding an induction motor is carried out. With the obtained mathematical results it is possible to reproduce the distorted current waveforms injected by the whole drive system in the grid. Finally the simulation results are compared with the real harmonic distortion generated by a variable speed drive.

New control strategies for longwall armored face conveyors

This paper investigates a new control approach for longwall armoured face conveyors (AFCs) using variable speed induction motor drives (VSDs). Traditionally AFCs have used fixed speed or two speed motors, with various mechanical solutions employed to try and solve the problems that this causes. The VSD approach to the control problem promises to solve all the significant problems associated with the control of AFCs. This paper presents the control algorithms developed for a VSD base AFC drive system, and demonstrate potential performance via computer simulation.

Influence of Switching Frequency and Squirrel Cage Design on Audible Noise and Losses in Variable Speed Induction Motor Drives with Transistor and IGBT Inverters

A large number of experiments are performed to analyse the influence of the inverter type and the switching frequency on the audible noise, losses and overall efficiency in induction motor drives. Temperature measurements both in stator and rotor give an indication of the required derating, if any. Results for a standard design motor, consecutively supplied by a transistor based inverter and IGBT inverter are compared with the behaviour when the machine is directly connected to the mains. To analyse the influence of the rotor design, a special rotor with no current redistribution is constructed and mountedin a rewound stator. Higher switching frequencies have a large influence on audible noiseand temperature, but the overall efficiency remains nearly constant. However the distribution of losses is influenced.

Direct self control of induction machines fed by a double three-level inverter

For variable speed induction motor drives with very high power and extreme demand on the quality of torque, a novel concept of feeding an induction machine with open windings by two gate-turn-off (GTO) three-level inverters is investigated. For optimal operation with the restricted switching frequency of these high-power inverters, direct self control (DSC) is mostly suited, which is well proven with two-level and three-level inverters in traction, allowing a highly dynamic control of the induction machine. In comparison with two-level and three-level inverters, torque ripple and distortion of motor currents are efficiently reduced, while maintaining the excellent dynamic qualities of DSC.

Vector‐controlled induction motors using neural network

AbstractSlip‐frequency vector control generally is used for variable speed induction motor drives due to its excellent response characteristics. However, it is sensitive to the variation of motor parameters since the flux current and slip‐frequency commands are computed using the motor parameters. As a result, the system performance will be degraded if the controller parameters do not match the motor parameters.The authors propose a new approach of vector control in which quick responses and system robustness are obtained concurrently by the learning capabilities of neural network. In the newly developed method, controller parameters are learned in real time at medium and high speeds. Using these learned parameters, the low‐speed performance of the controller can also be improved greatly.This paper describes the theoretical analysis, simulation and experimental results of the proposed method.

A hybrid inverter/cycloconverter-based variable-speed three-phase induction motor drive for single-phase inputs

This paper presents a simple converter topology for driving a three-phase induction motor with a single-phase AC supply. Using only two active switches and a triac, the converter can start the motor with high starting torque and low input current, and can bring the motor up to full speed using a very cost-effective, single-phase field-oriented control strategy. The converter supplies balanced output voltages at rated frequency with virtually no output distortion and with very high input power factor. In this paper, the capability contours for different speed ranges and various operating modes are addressed; the trade-offs between output torque, torque ripple, input current distortion, and inverter rating are also explained, and the proposed control approaches are supported by simulation and test results. >

Minimization of acoustic noise in variable speed induction motors using a modified PWM drive

This paper describes an effective way of reducing acoustic noise in a motor supplied from an adjustable speed PWM drive. The PWM patterns are selected to eliminate the most acoustically sensitive harmonics in the motor's vibration spectra. This permits the PWM drive to use more economical yet slower switching devices while maintaining quiet operation. This method is applicable to both voltage source and current source inverters since the current waveform is used as the basis for eliminating the objectionable harmonics.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Acoustic noise of electromagnetic origin in an ideal frequency-converter-driven induction motor

With the advent of power electronics, there has been increasing demand for variable-speed drives in industrial applications because significant energy savings can be achieved. However, the use of frequency converters in driving induction motors has resulted in significant increase in acoustic-noise radiation. While there have been numerous studies on the acoustic-noise-generation mechanisms in variable-speed drives, the problem remains unsolved. The increase in acoustic-noise radiation in inverter-fed induction motors has been mainly attributed to the time harmonics introduced by the converters. A general algorithm is presented to compute the change in sound-power level of a variable-speed induction motor due to the change in the speed of operation in the absence of time harmonics (i.e. driven by an ideal frequency converter). General qualitative results based on this algorithm indicate that, even if an ideal converter can be designed to eliminate all the time harmonics, the acoustic-noise radiation of electromagnetic origin can still be significantly increased by the change in speed. This algorithm can therefore be used to help establishing the lowest limit of acoustic-noise radiation which can ever be achieved independent of frequency-converter configurations for a variable-speed induction motor.

Applied nonlinear control of an induction motor using digital signal processing

In this paper, the application of nonlinear input-output linearization techniques to the control of induction motors is presented. Practical issues concerning discrete-time implementation, rotor flux observation and stator current limitation are presented. The use of a high-speed digital signal processor (DSP) is particularly appropriate, facilitating a small sampling period and advanced control algorithms. Our control scheme is implemented on an industrial induction motor variable speed drive. Practical results are given showing the feasibility of the approach. >

Slip Frequency Control of Sinusoidal Current Regulated PWM CSI-Induction Motor by using Speed and Current Estimations.

For a variable speed induction motor drive, the control system without a speed sensor and a PWM current source inverter have been proposed. For this system, a voltage sensor and a current sensor are required instead of the speed sensor. The motor speed can be estimated by the measured instantaneous values of the voltage and the current. Since the PWM current source inverter is clearly superior to the PWM voltage source inverter in terms of voltage and current waveforms, i.e., sinusoidal waveforms, a more accurate estimation of the speed can be achieved.In this paper, the PWM current source inverter-induction motor drive without a speed sensor is presented, The used inverter can regulate the output current by PWM control under a fixed input dc current. The quick regulation of the ac current is achieved in this system because of the no influence of the dc link parameters. The effect of the filter capacitor in the inverter circuit on the current regulation is discussed. To eliminate the ac current sensors of the motor, the relationship between the inverter currents and the motor currents is made clear. The experiments show that the system without the ac current sensors has the same steady-state and transient characteristics as that of the system with the voltage and the current sensors.

Vector Controlled Induction Motors Using Neural Network.

Slip-frequency vector control generally is used for variable speed induction motor drives due to its excellent response characteristics. However, it is sensitive to the variation of motor parameters since the flux current and slip-frequency commands are computed using the motor parameters. As a result, the system performance will be degraded if the controller parameters do not match the motor parameters. The authors propose a new approach of vector control in which quick responses and system robustness are obtained concurrently by the learning capabilities of neural network. In the newly developed method, controller parameters are learned in real time at medium and high speeds. Using these learned parameters, the low-speed performance of the controller can also be improved greatly. This paper describes the theoretical analysis, simulation and experimental results of the proposed method.

Control Methods for Reduction of DC Link Capacitor and Restarting at Instantaneous Power Failure in PWM Converter.

Rectifiers composed of diodes or thyristors have many harmonics in line currents. Recently, PWM converters have been actively studied to reduce the harmonics. In order to put them into practical use, not only PWM control method but also the following control methods must be established.(1) Method for reducing the capacity of dc link capacitor.(2) Restarting method from instantaneous power interruption.For reducing the capacity of do link capacitor, it is necessary to suppress the fluctuation of dc link voltage at a sudden change of load. In this paper, the load is inverter for variable speed induction motor drives. The load current of converter, that is the inverter input current, is detected without delay time and ripple by multiplying the inverter output currents or motor currents and the inverter PWM signals. By adding the detected signal to do link voltage control loop as a compensating component, the fluctuation of dc link voltage at a sudden load change can be suppressed. As a result, the capacity of the dc link capacitor or can be reduced to smaller than one-fifth of that in the conventional diode rectifier. For restarting from instantaneous power interruption, the very simple control method is proposed. When the dc link voltage becomes low limitation value setted at a little bit lower than that obtained in diode rectifier in the period of power interruption, the PWM signals to converter are blocked. After recovery from power interruption, when the dc link voltage reaches the low limitation value, the PWM control signals are supplied to the converter again and it is restarted the operation. From the experimental results, it was confirmed that the PWM converter can be restarted from the instantaneous power interruption very smoothly.

低温ヘリウムブロワ

A helium blower that can pre-cool superconducting magnets with helium gas at a temperature of 80K was developed. The blower incorporates self-acting gas journal bearings, Rayleigh step-type thrust bearings, a variable-speed induction-motor drive, and a backward impeller. The performance of the blower was measured in a vacuum chamber containing a tank of liquid nitrogen and two heat exchangers. Tests results show that pressure ratio is more than 1.2 and adiabatic efficiency is 61% at design point (mass flow rate of 0.005kg/s and rotational speed of 130, 000rpm). Moreover, for testing bearing reliability, the blower shaft could be successfully driven at up to 148, 300rpm and a start-stop test was done more than one hundred times, but there were no troubles with the shaft or bearings.

Noiseless variable-speed squirrel-cage induction motor

A variable-speed squirrel-cage induction motor is proposed. It is made up of a squirrel-cage rotor and two stators, one of which can be turned for speed control. The proposed motor has the following special features: (1) The range of speed control is extremely wide and the motoring operation is almost constant-torque under constant supply source voltage and frequency. (2) No special source such as an inverter is required; (3) Smooth operation from starting to the rated speed can be expected without any special starter because of suppressed starting current and large starting torque. The results of a theoretical analysis and experiments on a test motor are given, and the characteristics of the motor are discussed. >

A new PWM speed control system for high-performance AC motor drives

An approach to speed control for AC motor drives that uses programmed PWM (pulse width modulation) switching patterns over the complete range of output speed is presented. The scheme provides smooth operation during the required switching-pattern changes and guarantees high-quality output voltage and current in the AC motor load, making it most suitable for high-performance, high-efficiency applications. A detailed description of the scheme and its realization is provided. Results of an experimental investigation on a variable-speed induction motor and a permanent-magnet synchronous motor drive system illustrate the advantages of the scheme. >

Slip Frequency Control Type Vector Control of an Induction Motor Using Numerical Data Processor

As a method of variable-speed induction motor drives, there is newly developed vector control method. The vector control method is made by controlling flux current component and torque current component of stator current vector, respectively. Since the flux component is parallel with rotor flux vector and the torque component is perpendicular with the flux vector, the control method is characterized by decoupling between the components of flux and torque.In the vector control method, there are field-orientation method (rotor flux vector detection type-vector control method) and slip frequency control type vector control. A flux detector is required in the field-orientation method, and therefore, the slip frequency control type vector control has been made by a 16-bit personal computer using numerical data processor. Then, the vector controlled induction motor shows good dynamic performance. This paper describes the theory and experimental results.

Methods of Evaluation of Harmonic Levels in Industrial Plant Distribution Systems

Techniques for analyzing and evaluating the harmonic levels in an industrial facility's electrical distribution system are presented. The various system models and types of harmonic source representation are described. A harmonic evaluation should be performed when a new industrial facility will include sources of harmonics or when the addition of harmonics injecting equipment is being considered. Cogenerators and variable-speed ac induction motor drives are examples of sources of harmonics that are growing in size and number. The methods described utilize a harmonics load flow program based on the direct solution of the impedance matrix at each harmonic frequency. The program includes detailed models of transformers, lines, loads, and generators. It also allows the specification of the harmonic sources by either ac/dc converter parameters or by sampled data of the current or voltage waveform. Results from the analysis of two typical distribution systems in large industrial plants are presented. This analysis illustrates some of the problems that may be encountered and gives recommendations for solutions to these problems.

Detections of secondary current and torque of induction motors using amorphous microcore field sensors

New secondary-current sensors for squirrel-cage induction motors are presented using a multivibrator with two group amorphous microcores. The 8-pair micro cores are set near the both endrings of a rotor for cancellation of the influence of unstable rotor motion on sensing of the secondary current. Electromagnetic torque was detected as an output voltage of a multiplier for the secondary current and the main flux. The main flux was detected using a multivibrator-type flux sensor utilizing two stator teeth as two cores. A possible new control system for variable speed induction motors with a torque feedback loop is discussed, which stably works independently of variations of motor parameters.

Evaluation and comparison of two types of induction-motor drives

The evaluation of steady-state performance and the design methods for variable-speed inverter-fed induction-motor drives suitable for different industrial applications are complex. The nonlinear variation of the drive-system performance indices with frequency and filter parameters, the presence of special performance indices such as pulsating harmonic-torque components, the depletion of breakdown torque, and deterioration in the performance as low frequencies are approached etc. necessitate a completely different approach to the design of these drive systems as compared to the design of conventional single-speed machines. This paper is an attempt to evaluate and compare two types of optimal inverter-fed variable-speed induction-motor drives suitable for two different industrial applications. Digital-computer solutions for the results are presented.

Loss-optimal PWM waveforms for variable-speed induction-motor drives

The paper calculates and provides results on loss-optimal commutation tables suitable for application in digital PWM commutation steering circuits for variable-speed induction-motor drives. The work differs from other works on this subject, because a special induction-motor-loss model is incorporated into the PWM waveform optimisation procedure, and because optimised waveforms with up to seven commutations per quarter period are provided.