Development of sensorless MPPT for Wind Energy Conversion System using Z source converter

Abstract

The constantly increasing environmental concern about global warming and energy crisis have created a new demand
for clean and sustainable energy sources. Wind power generation experiences a rapid growth compared to solar power
generation. This paper presents a sensorless maximum power point tracking (MPPT) controller for wind energy
conversion system (WECS) involving a variable-speed wind turbine with a permanent magnet synchronous generator
(PMSG) and a Z-source inverter (ZSI). Generally induction generator are preferred in wind power conversion systems
as it has the advantages like rugged construction and less maintenance. But the main drawback is that it operates at
low-power factor and requires an AC excitation supply. PMSG machines can be used to overcome these drawbacks. The
output of PMSG is given to Power converters to get constant voltage and frequency. Basically there are three stages of
power conversion which includes rectification, DC-DC converter and inverter. As the number of stages increases
overall efficiency of WECS reduces. Therefore two-stage direct-drive WECS is adopted. A simple sensorless speed
estimator is used to estimate the rotor speed for different wind speeds. In this paper Perturb & Observe MPPT controller
is proposed for WECS using ZSI. This two-stage- based direct-drive system is simulated in MATLAB/SIMULINK. The
simulated results are analyzed for a standalone load and a grid. It is observed that a Z-Source is more power efficient
than a Buck-Boost converter, as there is no switching device present. Also WECS for 6 pulse ZSI and a novel Sparse
Matrix type ZSI were simulated and it was observed that the 6 pulses gives out less harmonics compared to the sparse
matrix type of Inverters. Since the Z-Source is less bulky and more efficient compared to the conventional buck boost
systems used, it is more viable to use the Z-Source inverter instead of the DC Chopper system.