A Modified Algorithm based on the Equal-Areas PWM for the Extend of Linear Operation of a Microprocessor-Controlled PWM-VSI

Fotis Konstantinos Paterakis, ,M Darwish,Koulouras E Grigorios,School Of Engineering And Design, Brunel University, London, Uk ,D Nafpaktitis

doi:10.21535/ijrm.v5i1.983

Abstract

A modified algorithm based on the Equal-Areas PWM (EAPWM) is being presented in order to extend the linear operation of the inverter in the overmodulation region, while improving the voltage output in terms of fundamental harmonic component amplitude and Total Harmonic Distortion (THD). EAPWM provides an alternative to Regular Sampling (RS) PWM and Space Vector PWM (SVPWM) strategies. EAPWM is a direct digital PWM method that uses the equal areas theorem to determine the pulse widths. This method maintains the commutations through a complete fundamental cycle, in contrast to naturally and regular sampling PWM techniques, where switched pulses progressively disappear for values of modulation index M greater than unity. In addition, this algorithm reveals several linear operating regions of controlling the output fundamental. Simulation and experimental work carried out using a single-phase voltage source inverter (VSI), showing less harmonic content is present for the first harmonic cluster at the switching frequency, compared to (RS) PWM and Space Vector PWM (SVPWM) strategies. This method is suitable for robotic applications where online control through a microcontroller is needed to drive rotating type loads such us ac motor drives and stepper motors.

Highlights

This paper proposes an alternative solution to extend the linear operation of the inverter, by modifying the algebraic algorithm of Equal-Areas pulse width modulation (PWM) (EAPWM) that was first introduced in [17]-[18]
A modified algorithm based on the EAPWM capable of expanding the linear operation of the inverter while penetrating the overmodulation region in a linear manner has been presented
Comparison with RSPWM and Space Vector PWM (SVPWM) has been showed the superiority of the proposed method in terms of Total Harmonic Distortion (THD) and low order harmonics

Summary

INTRODUCTION

Regarding the conventional sinus PWM (SPWM) which is the most widely used method in industry, in a three-phase PWM inverter this ratio is limited to 0.87 otherwise output fundamental is 87% of the input DC voltage To overcome this drawback of poor use of the input DC source significant research work has been undertaken revealing different concepts and performance [4]-[13]. Instead of introducing triplen harmonics to gain the ability to increase the modulation index or creating discontinuity in the sinus reference waveform, it resets the modulation index only for the over-modulated region, to an optimum value of M in order to recalculate the pulse widths and retain the commutations while avoiding any overlaps.

REVIEW OF THE BASIC THEORY OF EAPWM

MODIFIED ALGORITHM

COMPARISON WITH OTHER PWM METHODS

EXPERIMENTAL RESULTS

CONCLUSIONS AND FURTHER WORK