Brushless Synchronous Generator-Unidirectional Rectifier for Offshore Wind Energy Conversion System

This paper presents the variable speed applications of a recently developed generator named Brushless Induction Excited Synchronous Generator (BINSYG) for offshore wind power applications. The machine is basically a Synchronous generator (SG) with its excitation fed from a three-phase Induction Machine (IM). Both the machines are embedded in the same machine frame and share the same magnetic core. The SG feeds power to the dc grid via a five-level Unidirectional Dual Flying Capacitor Active Neutral Point Converter. The converter is controlled such that the Total Harmonic Distortion (THD) of the current flowing through the stator of SG is below 5% and at unity power factor at SG terminal. The excitation developed by IM-type exciter is adjusted using a new control strategy that is proposed for Voltage Source Inverter, such that BINSYG can operate at wide speed range necessary for Wind Energy Systems (WES). The complete system is controlled without using ac voltage sensors and speed encoders. The proposed WES with its control algorithm is first modelled in MATLAB/Simulink. Further, rapid control prototyping verification in the form of real-time results using OPAL-RT is presented for a small scale (5.5 kVA) BINSYG feeding power to a 750 V dc grid.