Fixed frequency slide mode control for parallel multilevel inverters of DER’s in micro-grid (T-0451) (MFN 8593)

Abstract

With the increase in demand of electrical energy along with the increasing population growth rate and industrialization renewable energy resources play a vital role in breaching the gap between the demand and supply of power. Apart from the conventional energy sources i.e. fossil fuels etc., significant research is being conducted over renewable energy sources which are rich sources of green energy which is friendly to the eco-system and exist in abundance. Micro-grids play a key role in utilization of renewable energy resources and can be materialized locally near the electricity utility areas and at the same time reduces the transmission costs apart from the conventional grid. Though, micro-grid model is a handy tool for engineers in breaching the demand and supply gap of electricity, yet they face some complications. Therefore, a number of control mechanism and power electronic circuits are used in a micro-grid to make use of the renewable energy resources in a cost effective and efficient manner. A micro grid mainly operates in two different modes i.e. grid-connected mode and islanded mode. This mainly depends upon the availability of power from the conventional grid as well as the integration of different types of loads connected to the micro-grid and conventional grid either simultaneously or separately. This means for a load that can be reactive or combination of active and reactive load there must be sufficient reactive power from the source for smooth operation. Among the power electronic converter topologies, multilevel converters have gained much popularity recently due some advantages they hold. Multilevel inverters are used to reduce voltage stresses on the converter and carry high power to the output terminals of the converter at the same time. In multilevel inverter circuits, three phase NPC inverter is quite popular. It has got four switching devices and two clamping diodes in a single leg to make a three level output waveform for the inverter voltage and current. The increase in level of the inverter is advantageous because of reduced filter size at the output of the inverter. Multilevel inverter can be used for high power rating systems because of lower voltage stress on a single leg of the inverter. This research is focused upon micro-grid inverters, their control mechanism with the use of Fixed Frequency Slide Mode Control, and parallel operation of the inverters which are used in the micro-grid with proper active and reactive power sharing between the DGs. Although, slide mode control has got extensive features which make it a good approach for use in power electronic circuits, yet the chattering problem in conventional SMC approach remained a drawback in its design. The fixed frequency SMC approach enables us to operate the power converters by means of a fixed frequency PWM approach and the design of SMC involves equivalent control laws which enable us to attain the fixed switching frequency for the converter. Therefore, it is handy tool to reduce the chattering phenomena without disabling any features of SMC. There are different types of inverter circuits used in micro-grid, the one used here is a three-level neutral point clamped (NPC) inverter