Reduced cost low speed wind or hydro energy conversion system with twin stator windings induction generator

This paper analyses two running regimes of low speed twin stator windings induction generator (TSWIG), directly coupled to the shaft of the wind turbine. A single low cost (reduced power) active rectifier is used to deliver the energy to the dc grid for a large shaft speed variation. At the rated speed, the capacitor battery supplies the induction generator with entire reactive power reducing this way the apparent power of the active rectifier. When the turbine speed decreases, the capacitor battery capability also decreases but the active rectifier (inverter) could assist the generator magnetization because the turbine power reduction relieves the active power of the active rectifier. The paper also investigates the self excitation of the stand alone TSWIG in an emergency regime. Digital simulation proves the self excitation at rated wind speed as well at low wind speed with power limitation.

I. Introduction

Induction generators have been employed to operate as wind turbine generators and small hydroelectric generators in isolated power systems [1]–[3], due to the practical advantages related to low maintenance cost, better transient performance, ability to operate without DC power supply for field excitation, and brushless construction. With the development of the packaged high speed gas turbine and high speed diesel engine, it becomes increasingly awkward that the prime mover and the generator are connected by a gear reducer. On the contrary, a direct connection between the prime mover and the generator has many advantages, such as low noise, high efficiency, and high power density.