Design & Implementation of Parallel Operation of Inverters with Instantaneous Current Sharing Scheme Using Multiloop Control Strategy on FPGA Platform by Shahil Shah -Department of Electrical Engineering Indian Institute of Technology, Kanpur

Abstract
 In these days of acute shortage of conventional energy resources, the harness of renewable energy has received considerable attention. In general, power obtained from Renewable Energy Sources(RES) is not of the form which is directly deliverable to the AC load or the utility grid. Voltage Controlled Voltage Source Inverters (VCVSI) forms the interface link which conditions power to the form deliverable to grid or load. To modularize the system, instead of a single inverter, the use of number of parallel inverters of reduced rating is proposed. The parallel operation of inverters in RES system o ers advantages like reliability and redundancy in addition to the low maintenance cost of a low power unit compared to that of high power unit. However there is a need of control strategy to strictly hold the amplitude, phase and frequency of output voltages of inverters at the same values in order to avoid circulating currents through inverter modules and make them share load currents equally even during transients. In this thesis work a control scheme is proposed and implemented for paralleling of three phase inverters which enables the inverters to share load currents equally even during transients (instantaneous current sharing), and also track the sinusoidal voltage reference. This voltage reference is either free running or is derived from grid voltage so as to feed AC load or to synchronize the module with any utility grid. The design issues for designing of multiloop control structure are analyzed at length with the discussion of active damping to increase the damping and relative stability of system. Design of outer current sharing controller has been done and its design intricacies are included in the work. FPGAs can be used to control power electronic systems. They have advantages like high speed, parallel processing capability, and rich digital I/O interface. In this thesis, basic modules required for development of controllers for power electronic systems are developed and tested with standard signals. The proposed control scheme for parallel operation is implemented for two 3-phase inverters using this FPGA platform.
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