M.A. Rahman

Harmonic minimization in delta modulated inverters using tuned filters

The integrator in the modulator of delta PWM inverters acts as a filter to estimate the input reference signal from the output waveform for comparison purposes. The use of a tuned filter allows the online variation of filter cutoff frequency and ensures minimization of desired harmonics from the output of the inverter. This method is particularly suitable for delta-modulated inverters used in variable-frequency applications. The modulators harmonic performance has been studied using a windowed discrete Fourier transform. The theoretical results were verified experimentally. The significance of the modulator lies in its simplicity, versatility, and ease of online harmonic minimization, which is achieved without predetermination of the switching points.<<ETX>>

Experimental Performances of the Single-Phase Wavelet-Modulated Inverter

This paper presents the real-time implementation and experimental performances of the wavelet-modulation technique for single-phase voltage-source (VS) inverters. The wavelet-modulation technique is realized through constructing a nondyadic-type multiresolution analysis, which supports sampling of a sinusoidal reference-modulating signal in a nonuniform recurrent manner, then reconstructing it using the inverter-switching actions. The required nonuniform recurrent sampling is carried out by using dilated and translated sets of wavelet basis functions, which are generated by the scale-base linearly combined scaling function. The reconstruction of the sampled signal is accomplished by using dilated and translated sets of wavelet basis functions, which are generated by the scale-base linearly combined synthesis scaling function. The dilated and translated sets of wavelet basis functions used in the reconstruction are employed as switching signals to activate the inverter-switching elements. The wavelet-modulation technique is implemented in real time by using a digital signal processing board to generate switching pulses for a single-phase VS H-bridge (four-pulse) inverter. Experimental performances of the single-phase inverter, which is operated by the wavelet-modulation technique are investigated while supplying linear, dynamic, and nonlinear loads with different frequencies. Experimental test results show that high magnitude of fundamental components and significantly reduced harmonic contents of the inverter outputs can be achieved using the wavelet-modulation technique. The efficacy of the developed modulation technique is further demonstrated through performance comparisons with the pulsewidth- and random-pulsewidth-modulation techniques for similar loading conditions.

Analysis of delta PWM static AC-DC converters

An analysis and implementation of delta modulation (DM) technique in the control of AC-DC converters are presented in this paper. The DM technique offers advantages of easy implementation, continuous converter voltage control, and a direct control on the line harmonics. A simple model of the delta modulator is proposed to predict switching frequency, identify dominant harmonics, and determine switching points of the converter waveforms. Results of parametric variations of the modulator and performances of the single and three phase DM converters are reported. Experimental results of the single and three phase DM AC-DC converters validate the analytical results. >

PERFORMANCE OF HYSTERESIS PERMANENT MAGNET MOTORS

ABSTRACT There is an increasing interest in using permanent magnet (PM) hysteresis motors because of their superior performances over the conventional hysteresis motors. Recent NdBFe magnets have the advantages of higher magnetic energy product and remanence. It can develop significant accelerating torque during run-up and synchronization with limited temperature tolerance. The application of the NdBFe magnets in electrical machines Is attracting wide attention. This paper presents the perspective of NdBFe magnets in the application to hysteresis motor with a view to improve the overall performance of such motors. Simulated and measured performance characteristics for steady-state operation and transient response are given. Results presented bring out significant Influences on the run-up and synchronization performances of such type of motors. Using the common stator frame of a 3-phase Mawdsley generalized machine, a performance comparison between the PM hysteresis motor and circumferential-flux hysteresi...

PERFORMANCE ANALYSIS OF SELF-EXCITED INDUCTION AND RELUCTANCE GENERATORS

ABSTRACT The paper presents a suggested method for ac power generation from a constant speed drive using capacitor excited induction and reluctance machines. The proposed arrangement is adapted to use one stator frame and two rotor types, namely, salient poles reluctance and squirrel-cage induction rotors. Operational and steady-state equivalent circuits for both types are developed and used to predict the dynamic and steadystate behaviours under load conditions. This analysis depends mainly upon the computation of the power angle for a given machine parameters, capacitor ratings, and load conditions at a constant speed. Further, stability limits of both generators are investigated by developing the active-reactive power (P-Q) diagram for each generator. Conditions required to achieve self-excitation are also given. Performances of the two generator types are evaluated theoretically and experimentally.

Discrete time-based model of the sinusoidal pulse width modulation technique

This paper presents a novel mathematical model for the sinusoidal pulse-width modulation (SPWM) technique. The proposed mathematical model is based on the sampling theory and discrete-time signal processing tools. In this model, the carrier signal is represented as a non-uniform sampling function, while the switching actions are viewed as an interpolating process. The proposed mathematical model is used to simulate a single phase SPWM voltage source inverter. The simulation results are compared to the conventional SPWM model for the same inverter. The match between the results of the proposed and conventional SPWM models validates the accuracy of the new mathematical model

Wavelet-based dynamic voltage restorer for power quality improvement

This paper presents a novel method for power quality improvement employing wavelet analysis. A wavelet filter bank is used to detect and classify various disturbances experienced by the voltage on the load side. A dynamic voltage restorer is used to compensate the voltage under disturbance conditions and maintain the rated load voltage. The input and the output voltages of the DVR are both controlled by the wavelet filter bank outputs. The approximations control the input voltage to the AC-DC converter. The control pulses of the DC-AC inverter are controlled by the details. Different types of disturbances are simulated to test the performance of the proposed control scheme. The proposed wavelet based control scheme successfully provided fast and accurate voltage restoration following any form of transient disturbances.

Performance of a hybrid current-controlled VSI fed permanent magnet synchronous motor drive

Permanent-magnet synchronous motors are widely used in modern variable speed AC drives. This is achieved by using a current controlled PWM voltage source inverter (VSI) system. In this paper, both the hysteresis current controller and the ramp comparator are presented and their performances are evaluated. Each current control scheme has its own advantages and drawbacks throughout the entire range of speeds. A hybrid controller, in which a combination of a hysteresis controller for high-speed operation and a ramp comparator controller for low-speed operation is proposed to overcome the drawbacks of each controller. Comparative performances of the different types of current controllers under vector control technique are presented. The proposed scheme gives significant improvement in the system performances over existing methods.

An optimum delta modulation strategy for inverter operation

An improved PWM inverter waveform synthesis technique for harmonic control in delta modulation (DM) process is presented. Filtering approach is incorporated in the DM technique to reduce harmonics of lower frequencies and suppress the unwanted subharmonics. Analytical method is described to determine the performance of multistage delta modulated inverter and the results are substantiated by experimental verification.

Modern electric motors in electronic world

The combination of developments in power electronics, magnetic materials, microcomputers and controls has significantly advanced the design, manufacture and applications of electric motors. Innovative configurations of modern motors, power semiconductor converter topologies and computer control strategies form the core of todays electric drive technologies. A system review of modern electric motors in the context of industrial electronics is briefly presented. Reliable and efficient electric motors are the workhorse of the modern industrialized world and hence ongoing markets for electric motors are assured.<<ETX>>