Matlab GUI program

A graphical user interface (GUI) is a graphical display that contains devices, or compo- nents, that enable a user to perform interactive tasks. To perform these tasks, the user of the GUI does not have to create a script or type commands at the command line. Often, the user does not have to know the details of the task at hand.

The GUI components can be menus, toolbars, push buttons, radio buttons, list boxes, and slidersjust to name a few. In Matlab, a GUI can also display data in tabular form or as plots, and can group related components.

In order to test the peripheral auxiliary circuit of F28335 and the RTDX, some communication programs have been made in Matlab by using the graphical user inter- face. These programs have been developed for the testing of ADC, digital input, digital output and PWM, respectively. The interface of the control panel is shown in Figure 3.12 and the partial codes are clearly set out in Appendix C.

Chapter 4

Maximum Power Point Tracking

Wind power has been regarded as one of the main alternative renewable power sources to fossil fuels. Many countries have set strategic plans to develop technology for utilising wind power and a lot of researchers have shifted into this area. During the last decade, more and more attention has been paid to utilising renewable energy sources to tackle the energy crisis we are facing. Wind power has attracted most of the attention and many countries have launched various initiatives to increase the share of wind power in electricity generation.

Normally, wind generation systems can be divided into variable-speed generation systems and xed-speed generation systems. Variable-speed generation systems are more attractive than xed-speed systems due to improved wind energy production and reduction of the icker problem. The eciency of the wind turbine is higher than conventional ones. However, it does not mean that the actual eciency is always high. It depends on the control algorithm used to extract the output power from the wind turbine. An advanced technique will be designed to extract the maximum power from the wind turbine under all working conditions. In variable-speed generation systems, the wind turbine can be operated at its maximum power operating point for various wind speeds by maintaining the tip speed ratio at the value that maximises aerodynamic eciency. In order to achieve this ratio, the permanent magnet synchronous generator load line should be matched very closely to the maximum power line of the wind turbine generator. A variety of control schemes have been studied in order to produce as much power as possible from various wind speeds.

During the last few decades, many dierent maximum power point tracking control strategies have been developed. Among the MPPT methods, the hill-climbing method

L Grid C1 C2 PMSG 3-Phase Inverter LCL Filter

Figure 4.1: Topology of the system.

for comparing kW variation is the simplest but least ecient [13]. [14] developed a fuzzy controller for tracking the generator rotor velocity corresponding to the wind speed to extract the maximum power. Tan and Islam presented three sensorless control methods: wind prediction, the xed voltage scheme for the inverter and current- controlled inverter [15]. An advanced hillclimb searching method, taking into account the wind-turbine inertia, was proposed in [16]. Datta and Ranganathan developed a generator velocity reference, which is dynamically modied in accordance with the magnitude and direction of change of active power [17]. [18] presented a method considering the duty cycle of the DC-DC buck-boost converter as a control variable. [19] presented a method of adjusting the duty cycle of the DC-DC buck-boost converter by using the gradient approximation algorithm. Many papers have adopted a boost converter to implement MPPT with dierent control strategies [20, 21].

4.1 System Congurations

The wind turbine system studied in this chapter is shown in Figure 4.1. It includes a wind turbine, a permanent magnet synchronous generator, a three-phase bridge rectier, a boost DC-DC converter and a voltage source DC-AC inverter. In order to simplify the MPPT analysis, commonly used DC-AC inverters will not considered, instead, a resistor is connected directly. The resistor provides a virtual load for consuming the real power generation.

The AC output from the PMSG is rectied into a DC signal by three-phase diode rectier circuits. The boost converter comprises an inductor, an IGBT switch and a diode. This converter divides the DC bus into two parts: the DC bus voltage at the

output terminals of the diode rectier, which is a variable DC bus voltage, and the DC bus voltage at the input terminals of the voltage source inverter, which is fed from a xed DC bus voltage. The output current of the generator-rectier system can be controlled by changing the duty cycle of the switch. Its purpose is to control the rectier output current, and therefore the generator current and torque, so that the maximum power can be captured from the wind by the turbine. The duty cycle of the boost converter is the only control variable for achieving MPPT.