Position Sensorless Control of Switched Reluctance Generator for Wind Energy Conversion

Abstract
This paper presents a novel sensorless control system of switched reluctance generator (SRG) in order to reduce cost, simplify system structure and increase reliability. Considering nonlinear characteristics of SRG and robustness of sliding mode observer (SMO), sensorless control method of SRG based on SMO is proposed and analyzed. For wind energy conversion system (WECS), a voltage-source PWM inverter is used to make power output of SRG connect to the grid (or ac load). The SRG phase current was regulated by current chopping control method (CCC). An 18.5kW three-phase 12/8 SRG experimental prototype was constructed and wind turbine mover was emulated using a DC motor drive. Test results using dual TMS320F2812 DSP as control core verified validity and feasibility of the proposed system. Keywords-switched reluctance generator; sensorless; sliding mode observer; DSP
I. INTRODUCTION
Switched reluctance generator (SRG) is a competitive candidate in the field of wind power generation, its inherent advantages make SRG to be more concerned in the emerging technologies and SRG has been applied to sourcing aerospace power systems [1][2], starter/alternators for hybrid vehicles [3], and wind energy conversion systems (WECS) [4]. Due to its main features, SRG is fit for the wind power utilization applications, which is characterized by low-speed high-torque operation. (1) Neither windings nor permanent magnets on the rotor support high-speed and high temperature, and also leading to low cost and high reliability, (2) The absence of windings on the rotor and simpler concentrated windings on the stator help to keep the majority losses within the stator, making SRG relatively easy to cool, (3) In order to capture maximum wind power and improve the utilization efficiency of wind energy, wind turbines must coordinate with generator, several controllable parameters of the SRG make it easy to obtain optimal power output, (4) SRG has no independent excitation windings, but replaced by the stator windings, excitation and power generation were controlled by time-sharing method through the controller, simplifying the controller structure, (5) Non-electrical coupling between SRG independent phases so that fault-tolerant capability has been greatly enhanced. Traditional SRG system is dependent on rotor position and a shaft position sensor becomes an integral part of control. However, position sensor increases cost and decreases system reliability, restricting the application of wind power generation of SRG. A cross section view of three-phase 12/8 poles SRG is shown in Fig.1. Fig.2 shows idealized inductance profile of SRG. When ignoring saturation, the inductance varies linearly with respect to the rotor position. As for three-phase 12/8 poles SRG, the inductance is minimum when stator and rotor poles are completely unaligned (0 degree) and maximum when poles are fully aligned (22.5 degree). Motoring status is obtained when the stator is excited during the positive slope in the inductance profile. And for generator, the stator phases are excited during the negative slope in the inductance profile.

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