Load voltage control and maximum power extraction of a stand-alone wind-driven PMSG including unbalanced operating conditions

This paper presents a control strategy to enhance the performance characteristics of a stand-alone wind-driven Permanent Magnet Synchronous Generator (PMSG) under different operating conditions. The presented control strategy aims at regulating the load voltage, in terms of magnitude and frequency and extracting the maximum wind-power under both constant wind-speed and variable wind-speed including both balanced and unbalanced loading conditions. The wind generating-system under study consists of a wind turbine, PMSG, switch-mode rectifier (three-phase uncontrolled rectifier followed by DC-DC boost converter), bidirectional DC-DC buck-boost converter, battery bank, three-phase SPWM inverter, LC filter, three-phase isolating transformer and three-phase load. The employed control strategy is firstly based up controlling the duty cycle of the DC-DC boost converter, included in the switch mode rectifier, in order to extract maximum wind-power. Then, the operating mode (charging or discharging of the battery bank) of the bidirectional DC-DC buck-boost converter is controlled to attain an appropriate constant dc-voltage under different operating conditions. Finally, a sinusoidal pulse width modulated (SPWM) inverter is used to regulate the magnitude and frequency of the load voltage via controlling the modulation index. A sample of simulation results is obtained and analyzed in order to check the capability of the presented control strategy of the employed wind generating-system. The presented simulation results verify the effectiveness of the presented control strategy to supply the load at constant voltage and frequency with maximum wind-power extraction under different operating conditions.