This thesis begins with providing a basic introduction of electricity requirements for small developing
country communities serviced by small scale generating units (focussing mainly on small
wind turbine, small Photo Voltaic system and Micro-Hydro Power Plants). Scenarios of these
small scale units around the world are presented. Companies manufacturing different size wind
turbines are surveyed in order to propose a design that suits the most abundantly available and
affordable turbines.
Different Maximum Power Point Tracking (MPPT) algorithms normally employed for these
small scale generating units are listed along with their working principles. Most of these algorithms
for MPPT do not require any mechanical sensors in order to sense the control parameters
like wind speed and rotor speed (for small wind turbines), temperature and irradiation (for PV
systems), and water flow and water head (for Micro-Hydro). Models for all three of these
systems were developed in order to generate Maximum Power Point (MPP) curves. Similarly,
a model for Permanent Magnet Synchronous Generators (PMSGs) has been developed in the
d-q reference frame. A boost rectifier which enables active Power Factor Correction (PFC) and
has a DC regulated output voltage is proposed before implementing a MPPT algorithm. The
proposed boost rectifier works on the principle of Direct Power Control Space Vector Modulation
(DPC-SVM) which is based on instantaneous active and reactive power control loops. In this
technique, the switching states are determined according to the errors between commanded and
estimated values of active and reactive powers.
The PMSG and Wind Turbine behaviour are simulated at various wind speeds. Similarly, simulation
of the proposed PFC boost rectifier is performed in matlab/simulink. The output of these
models are observed for the variable wind speeds which identifies PFC and boosted constant DC
output voltage is obtained. A buck converter that employs the MPPT algorithm is proposed
and modeled. The model of a complete system that consists of a variable speed small wind
turbine, PMSG, DPC-SVM boost rectifier, and buck converter implementing MPPT algorithm
is developed. The proposed MPPT algorithm is based upon the principle of adjusting the duty
ratio of the buck converter in order reach the MPP for different wind speeds (for small wind turbines) and different water flow rates (Micro-Hydro).
Finally, a prototype DPC-SVM boost rectifier and buck converter was designed and built for a
turbine with an output power ranging from 50 W-1 kW. Inductors for the boost rectifier and
buck DC-DC converter were designed and built for these output power ranges. A microcontroller
was programmed in order to generate three switching signals for the PFC boost rectifier and one
switching signal for the MPPT buck converter. Three phase voltages and currents were sensed
to determine active and reactive power. The voltage vectors were divided into 12 sectors and a
switching algorithm based on the DPC-SVM boost rectifier model was implemented in order to
minimize the errors between commanded and estimated values of active and reactive power.
The system was designed for charging 48 V battery bank. The generator three phase voltage
is boosted to a constant 80 V DC. Simulation results of the DPC-SVM based rectifier shows
that the output power could be varied by varying the DC load maintaining UPF and constant
boosted DC voltage. A buck DC-DC converter is proposed after the boost rectifier stage in
order to charge the 48 V battery bank. Duty ratio of the buck converter is varied for varying the
output power in order to reach the MPP. The controller prototype was designed and developed.
A laboratory setup connecting 4 kW induction motor (behaving as a wind turbine) with 1kW
PMSG was built. Speed-torque characteristic of the induction motor is initially determined.
The torque out of the motor varies with the motor speed at various motor supply voltages. At
a particular supply voltage, the motor torque reaches peak power at a certain turbine speed.
Hence, the control algorithm is tested to reach this power point. Although the prototype of
the entire system was built, complete results were not obtained due to various time constraints.
Results from the boost rectifier showed that the appropriate switching were performed according
to the digitized signals of the active and reactive power errors for different voltage sectors.
Simulation results showed that for various wind speed, a constant DC voltage of 80 V DC is
achieved along with UPF. MPPT control algorithm was tested for induction motor and PMSG
combination. Results showed that the MPPT could be achieved by varying the buck converter
duty ratio with UPF achieved at various wind speeds.
| Identifer | oai:union.ndltd.org:canterbury.ac.nz/oai:ir.canterbury.ac.nz:10092/8608 |
| Date | January 2013 |
| Creators | Acharya, Parash |
| Publisher | University of Canterbury. Electrical and Computer Engineering |
| Source Sets | University of Canterbury |
| Language | English |
| Detected Language | English |
| Type | Electronic thesis or dissertation, Text |
| Rights | Copyright Parash Acharya, http://library.canterbury.ac.nz/thesis/etheses_copyright.shtml |
| Relation | NZCU |
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