Reduction of Harmonics in Electronic Ballast Using Buck Boost Converter

This paper is based on the design and analysis of Total Harmonic Distortion(THD) and power factor for Compact Fluorescent Lamp. In the proposed electronic ballast Buck Boost converter operates in the continuous conduction mode, which provides a constant DC voltage to drive the lamp.By choosing the switching frequency more than the resonant frequency the zero voltage switching is achieved in resonant inverter. The design and simulation of the proposed topology using MATLAB-Simulink for the rms value of 220 V the total harmonic distortion is reduced by 15% and the power factor is improved to 0.98. KEYWORDS— Buck Boost converter, THD, Power Factor. INTRODUCTION In earlier days the incandescent light is dominated in the lighting industry. But due to their low level of lumen capacity and efficiency the consumption level is reduced to improve that high power factor LED and CFL bulbs have been introduced. The LED has more advantages with long lifetime, robustness, and small size, but in cost it was economically high and also need more concentration on heat management. Due to overheating of LED bulbs there may be a possibility of device failure. To overcome these issues CFL proves itself to be superior to the LED bulb. Generally, all lamps required adequate voltage for ignition at the time of starting current limiting control which essentially creates a negative impedance characteristic. In CFL lamp, to reduce the negative impedance characteristics the ballast is used to provide the constant voltage for ignition. Magnetic ballast made up of magnetic core and is larger in size produces a core and iron losses. It results the lagging power factor due to the inductive coil. So electronic ballast is used to perform the PFC for stable operation in high frequency. In real time application the ballast circuit requires peak current that leads to high crest factor which minimize the lamp life. Also the disadvantage in electronic ballast is, the occurrence of more spikes in a line current. However, mitigating of harmonic distortion caused by lamps is very difficult on the distribution system. Fig .1. Power consumption Vs Lumen In the existing system, electronic ballast the switching times of the rectifier and filter distorts the sinusoidal input current with the input current which produces a high magnitude of lower odd harmonics. This result in the large amount of reactive power from the utility side caused high energy consumption. To overcome these disadvantages, converter topology is implemented which single switch controlled by the PWM block. This proposed topology reduces the voltage stress and also avoids ripple current .By using Full bridge inverter the output voltage of lamp get decreases hence the half bridge inverter is proposed in the circuit for the high output voltage. A. DC-DC Converter Topology Electronic Ballast circuit consists of bridge rectifier, with capacitor followed that the resonant inverter produces a high ignition voltage. Moreover, due to an unstable current resulting a high distortion with low power factor. Power quality issues are reduced by reducing the various DC-DC converter topologies. The problem can be resolved by two stages: One is converting the AC mains voltage to regulate DC voltage and another one is to convert regulated DC voltage to AC BUCK BOOST CONVERTER Fig.2. Circuit diagram for Buck Boost converter The proposed electronic ballast consists of a buck boost converter with a resonant inverter which provides a constant ignition voltage .The half bridge inverter produces a square wave voltage and is fed to the lamp to the LC network for filtering the higher order harmonics. For reducing the switching losses, the switching frequency is kept more than the resonant frequency to achieve zero voltage switching. By operating the converter in DCM (Discontinuous mode Operation) the current reaches peak value which may affect the lamp[1].To avoid that, the converter operates in a CCM mode with control loop using the PI controller to maintain constant DC voltage as source. Two switches are required while cascading the buck and boost converter [2] which results in switching stresses in the circuit. Therefore, in the proposed topology single switch converter topology is used to perform for reducing their stress. Srinivasan et al., International Journal of Advanced Engineering Technology E-ISSN 0976-3945 Int J Adv Engg Tech/Vol. VII/Issue II/April-June,2016/211-213 Fig.3 Circuit diagram for electronic ballast For the input source the normal sinusoidal input voltage is applied to amplitude Vm and frequency of 50Hz. ....(1) Duty cycle for the continuous conduction mode is