Comparison of a PWM Inverter and a Multilevel Inverter using the Switching Function Analysis for Harmonic Content and Efficiency

A conventional 3-level PWM Inverter and a Cascaded Multilevel Inverter, both rated at 230Vrms voltage output and 3KW are analysed using the Switching Function. The PWM signal for the 3-level inverter is derived by applying the Switching Function Technique to the equal area principle. For the Cascaded Multilevel Inverter the Switching Function Technique is initially applied to each H-bridge, and then added to derive the overall Switching Function for the Multilevel Inverter output. A new technique is employed to derive the pulse width of each H-bridge converter in order to construct the output voltage. Voltage expressions of the output voltages are derived for both topologies. The switching frequency is chosen to be the same for both inverters. To ensure the same number of commutations over a fundamental cycle for both inverters, the levels of the Multilevel Inverter must be properly selected to meet the PWM frequency of the conventional inverter. Frequency spectrum and expressions of THD of the output voltage are derived. The two inverters are compared in terms of THD and harmonic content of the output voltage. The efficiency is concluded from the number of switching instances and other parameters of the circuit

The Equal Areas Pulse Width Modulation (EAPWM) Method: An alternative approach to programmed PWM schemes

This paper investigates a direct approach to programmed PWM modelling directed to simplification of implementation. Analytical equations of Equal Areas Pulse Width Modulation (EAPWM) method are presented along with harmonic analysis results for odd number of pulses in half period of a 3-level single phase VSI. Simulation and practical work is being presented also. Estimation of the marginal modulation index has been carried out, inside the linear region of operation. The proposed method provides a rigid framework since it lies on a well-defined mathematical formulation without the need of large computational effort.http://www.journal.esrgroups.org/jes/papers/12_1_12.pd

Preventing school vandalism and improving discipline: a three-year study.

Vandalism is a major problem facing educators and taxpayers alike. The present investigation analyzed how vandalism costs and student disruption were related to the implementation of a training and consultation package designed to increase the reinforcing ambience of the school. A positive environment, it was posited, would displace previous events that may have set the occasion for vandalism, with cues to promote productive school performance. Eighteen elementary and junior high schools were involved over a 3-year period. Using a delayed treatment control design, treatment was delivered following either 4 or 13 months of baseline. During treatment, teams of school personnel attended training workshops in behavioral strategies for reducing vandalism and disruption by students in school. Each team also met regularly on its campus to plan and implement programs on a schoolwide basis. To demonstrate that reinforcing procedures were actually implemented and accompanied by change in student performance, these variables were periodically probed throughout the study. Project staff also provided consultation. Vandalism costs decreased significantly (p less than .05) more in treatment than control schools, with an average reduction of 78.5% for all project schools. Rates of praise delivered by project teachers and other randomly selected teachers in the school increased significantly (p less than .05), and rates of off-task behavior by students decreased significantly (p less than .05) following treatment. The staff development model used in this study appeared to be both feasible and economical