Digital Implementation of Hybrid Active Power Filter for Power Quality Improvement Using Advanced Microcontroller

Abstract

Solid state rectification of AC power using diodes and thyristors are drawing harmonic current and reactive power from AC supply and behave as non-linear load. Due to the harmonics current present in system, which result into low power factor, derating of equipment, poor efficiency, high transformer and power line losses, interference in the communication network system, reduced system stability, and operation failure of electronic equipment. These all will raise serious issues related to power quality of the supply system. With the aim of mitigation of the same, the various types of power filters are selected and analyzed with different control algorithm under different line side and load side conditions. This thesis mainly focuses on the performance analysis of passive power filter, shunt active power filter, and hybrid active power filter for power quality improvement. The performance analysis of the filters in terms of reduction in percentage THD as per IEEE-519-1992 standard and unity power factor at line side under various line side and load side conditions. The proposed research work presents a design of 5th and 7th order tuned passive power filter, detailed modelling and performance analysis of the hysteresis current controller based shunt active power filter with different reference compensating current generation methods (e.g., instantaneous reactive power theory, synchronous reference frame theory, Fryze current computation) under different line and load side conditions. The system performance is analyzed and simulation results for the same is presented. This thesis also present the simulation analysis of hybrid active power filter with instantaneous reactive power theory and synchronous reference frame control algorithm. The proposed topology of hybrid active power filter consist of active power filter and passive power filter are connected in shunt with the mains feeding a nonlinear load. The shunt passive power filter is tuned to eliminate most dominate 5th order load current harmonic and shunt active power filter is used compensate all other higher order load current harmonics. This approach help to reduce the overall rating of shunt active power filter, and maintain unity power factor at line side with low THD, which makes system more economical for industrial usage. To handle the superior algorithmic needs in low cost embedded designs, ARM recently introduced in the market a new processor familythe STM32F4 ARM Cortex- M4. This new microcontroller (MCU) family emerges in the best in class of installed embedded system with low cost and low-power. In the field of active power filters main focus of research has been on development of novel techniques for reference compensating current generation in order to improve the compensation characteristic. In order to demonstrate the performance improvements brought by this STM32F407VGT6 advanced microcontroller, the Instantaneous Reactive Power theory algorithm is digitally implement for shunt active power filter. A laboratory scale prototype model of the sinusoidal PWM controller based twolevel shunt active power filter is developed using STM32F4VGT6 ARM Cortex-M4. Presented hardware results shows the effectiveness of shunt active power filter used to compensate harmonics and maintain unity power factor at line side with low THD. Also the compensation capability of shunt active power filter is demonstrated for steady state as well as transient conditions of operation. This research has further opened-up the scope for developing better current controllers for multi-level converter based shunt active power filters and hybrid active power filter for more precise compensation of harmonics and reactive power compensation.