Power Electronic Components and Electronic Converters Gave Birth to Numerous New Applications, Offering Unmatched Comfort, Flexibility and Efficiency to the Customers. Owing to The Improvement In Technologies, Large Number of Harmonics Are Introduced and They Degrade The Performance of the Three-Phase Four-Wire Distribution System. These Effects of Distortion Also Affect The Point of Common Coupling Where Other Loads Are Connected to the System. a Lot of Measures And Mitigating Techniques Have Been Presented In the Literature But Each Has Its Own Drawbacks Like Circuit Complexity, Lack of Reducing Lower Order Harmonics, Occurrence of Resonance Problems With Line Impedance, Etc. to Overcome These Defects, the Thesis Proposes Two Techniques to Improve the Power Quality of the System. the First Method Aims at Designing a Neutral Current Compensator and the Second Method Involves Designing of Unified Power Quality Conditioner. the Neutral Conductor of Three-Phase Four-Wire Distribution Systems Have Been Widely Employed to Deliver Electric Power to Single-Phase Or Three-Phase Loads. the Neutral Conductor Usually Carries the Zero-Sequence Current Due to The Unbalanced Loading Among Phase Conductors. As More and More Electronic Equipment Such As Computers, Copy Machines and Adjustable Speed Drives Are Being Used, the Harmonic Currents Drawn By Their Rectifier Front Ends Also Become Significant. Especially, the Zero-Sequence Triple (3Rd, 9Th, Etc) Harmonics Accumulate In the Neutral ...