An improved sensorless decoupled power control scheme of grid connected variable speed wind turbine generator

• Sensorless control of a DFIG-based wind turbine and multilevel inverter is presented.
• We develop a method based on modified–PLL to estimate the rotor position and speed.
• The algorithm is machine parameters insensitive and does not require any estimated quantities.
• Control of the rotor current by robust space-vector-based hysteresis current control (SVBHCC).
• The use of zero-voltage vectors reduces the average switching frequency.

This paper proposes an improved sensorless control for a variable speed-constant frequency generation system based on a doubly fed induction generator (DFIG). The rotor position and speed estimation method is based on a modified phase-locked-loop (MPLL). Using the measured stator voltages and rotor currents, the proposed algorithm can directly generates the rotor position and speed by simple arithmetic operations using the PLL basis. The speed is estimated independently of the machine parameters and the algorithm avoids using differentiation, which results in a substantial improvement in control robustness and improves its immunity to noise. This paper also presents the design of a space-vector-based hysteresis current control (SVBHCC) technique applied to a three level neutral-point-clamped (NPC) inverter to enhance the control system performance and achieve high power quality. The algorithm allows a systematic application of zero-voltage vectors that leads in reducing the average switching frequency. Furthermore, the space-vector-based approach reduces the interference between the commutations of the three phases. Simulation results confirm the effectiveness and validity of the proposed control approach.