Analysis & Design of Active Inductor
Power conditioning topologies such as adjustable speed drives (ASDs) have a growing demand in industry for improving efficiency and reducing energy costs. Apart from efficiency improvement, the power density of these converters has increased considerably and a smaller form factor is preferred by modern industrial plants. Power converters produce unwanted harmonics which deteriorate the grid current quality. To mitigate the adverse effects of such harmonics, filtering techniques such as active/passive filters and harmonic traps are employed. Passive inductors play an important role in these filtering topologies. However, in higher power/utility scale power conversion systems, due to lower switching frequency, the size and weight of passive inductor is large and they occupy considerable space. In industries such as offshore oil drilling and maritime transportation, size and weight requirements are strict and such bulky solutions are not desirable.
For such applications, an effective way to make passive components compact is to emulate using active devices. In this thesis, design of an Active Inductor for high power applications using an H-bridge topology is proposed. The performance of common filtering topologies such as LC and LCL with Active Inductor replacing a passive inductor is analyzed. The proposed topology emulates an inductance value which is linear for a wide range of operation, devoid of saturation issues and is compact in size and weight. Weight and volume analysis is done for an active topology and compared with equivalent passive inductors. It is shown that the emulated inductor is about 8 times lighter than a passive inductor of similar rating. Also, loss analysis proves that the topology has a high Q factor. A Zero Voltage Switching (ZVS) switching method is proposed to reduce switching losses further.
In addition, the dynamic behavior of the Active Inductor improves system performance during faults and disturbances. The value of inductance can be tuned to suit the requirements of the overall power conditioning circuit. The Active Inductor is shown to limit the current and voltage overshoots occurring due to faults. Simulation and experimental results from a laboratory prototype confirm the validity and utility of the proposed topology.