Research On Control Methods Of Stand-Alone Power Generation System Based On A Brushless Doubly-Fed Machine

The brushless doubly-fed machine(BDFM) is a new type of AC excited induction machine. Compared with the double-fed induction machine, the BDFM, without the brushes and slip rings, has the merits of wide operation speed range, long working life, low manufacturing cost, high reliability and low maintenance cost. The BDFM can be used for both grid-connected and stand-alone power generation, with broad application prospects in the field of wind power and ship shaft power generation. The BDFM stand-alone power generation system, composed of the BDFM and the AC excitation control system, is the sophisticated equipment with the combination of electrical machine, power electronics and numerical control technology.This research aims to study the BDFM stand-alone power generation system. In this paper, the effective mathematical models are established, the control methods are presented for symmetric loads and asymmetric loads, respectively, the phase-locked loop(PLL) technologies are investigated for dynamically tracking the amplitude, frequency and phase of the output voltage, the experiment platform of the BDFM stand-alone power generation system is built and the experimental research of the system operation control is carried out. The main contents of this paper include several aspects as follows:1. A new T-type steady-state model of BDFM is presented, which is more suitable for the performance analysis of BDFM stand-alone power generation system. The mathematical model of the stand-alone power generation system based on BDFM is established with the simulation analysis being implemented in Simulink. The characteristics of the power flow and the control winding current of BDFM is analyzed based on the T-type steady-state model, and the analysis results are verified by theoretical calculations and experiments.2. In order to dynamically track the amplitude, frequency and phase of the output voltage of the BDFM stand-alone power generation system, the PLL technologies for symmetrical and asymmetrical three-phase voltages are studied. The PLL, which is more suitable for the operation control of BDFM stand-alone power generation system, is developed based on the common synchronous ratating coordinate PLL. After carrying out a contrastive study on the two widely used PLLs for asymmetrical three-phase voltages, the new PLL for the operation control of the BDFM stand-alone power generation system under the asymmetric load conditions is presented.3. Based on the dynamic model of BDFM in rotary two-phase dq coordinate, the design principles of each control loop of control-winding side converter(CSC) are derived, and the complete control method of CSC under symmetrical load condition is presented. The mathematical model of supply side converter(SSC) at the synchronously rotating coordinate is deduced, and the current inner loop controller and the DC bus voltage outer loop controller are all designed with a complete SSC control method being presented.4. A dynamic model of BDFM based on double rotating dq coordinates is established for the asymmetrical load condition, and the control method of the BDFM stand-alone power generation system for supplying asymmetrical loads is proposed.5. A BDFM stand-alone power generation experiment system is designed. The performances of the control winding side LC filter and control winding current vector controller are verificated via experiments. The detailed experiments of the power generation system operation are carried out under symmetric and asymmetric loads, respectively, and the experimental results demonstrate the effectiveness of the proposed control methods.