DESIGN AND SIMULATION OF CASCADED H BRIDGE MULTILEVEL INVERTER USING GRID CONNECTED PV SYSTEM

Abstract

The continuous increase in power demands and need for a cleaner environment makes decentralized renewable energy production, like solar and wind, more and more interesting. Decentralized energy production using solar energy could be a solution for balancing the continuously-increasing power demands. This continuously increasing consumption overloads the distribution grids as well as the power stations, therefore having a negative impact on power availability, security and quality. One of the solutions for overcoming this is the grid-connected photovoltaic (PV) system. With the extraordinary market growth in grid-connected PV systems, there is increasing interests in grid-connected PV inverters. Focus has been placed on inexpensive, high-efficiency, and innovative inverter solutions, leading to a high diversity within the inverters and new system configurations. This report chooses cascaded multilevel inverter topologies for grid connected PV systems to reduce the cost and improve the efficiency. First, a single-phase cascaded H-bridge multilevel PV inverter is discussed. To maximize the solar energy extraction of each PV string, an individual maximum power point tracking (MPPT) control scheme is applied, which allows independent control of each dc-link voltage. A generalized non active power theory is applied to generate the reactive current reference. Within the inverter’s capability, the local consumption of reactive power is provided to realize power factor correction. Then, the modular cascaded H-bridge multilevel inverter is connected to a three-phase utility system and nine PV panels. Individual MPPT control is also applied to realize better utilization of PV modules. Also, mismatches between PV panels may introduce unbalanced power supplied to the three-phase grid-connected system. Thus, a modulation compensation scheme is applied to balance the three-phase grid current by injecting a zero sequence voltage. A modular cascaded multilevel inverter prototype has been built and tested in both the single phase and three-phase PV system. Simulation and experimental results are presented to validate the proposed control schemes. The targets of reducing the cost and improving the overall efficiency of the PV inverters can be achieved by applying the cascaded PV inverters and the proposed control schemes.