Study On Power Conversion Technology Of Distributed Power Generation System By Using High Speed Generator

The main advantages of the high speed machine are small size and high power density. However, the high speed machine suffers from higher loss density and cooling difficulty due to small cooling area, especially the high frequency harmonic currents produced by the power conversion system increase the loss and temperature of high speed machine. How to reduce the harmonic components is an important problem to be solved for the power conversion system design. The study of this thesis is a part of the project-"The study on distributed high speed generator system driven by micro-turbines and its energy conversion system", which is funded by the National Natural Science Foundation of China (No. 50437010). The study of the thesis is concentrated to the harmonics repression technology for high speed generator power conversion system. The main contents are listed as follows:(1) To reduce the current harmonics produced by the AC/DC power conversion and meet the requirements on self-starting, a PWM rectifier/inverter with current harmonics repression function is investigated. The mathematical model of small-signal is established. A special harmonic elimination pulse-width modulation (SHEPWM) strategy is utilized to overcome maximum switching frequency limit. The methods to solve switching angles are analyzed in the unipolar mode and bipolar mode respectively. Space voltage vector phase angle is determined by testing the zero crossing of line voltage, the no-error of current in the stable state is obtained through double closed loop. The simulation and experimental studies based on the above control strategies are carried out.(2) To overcome the maximum switching frequency limit and avoid complicated control scheme of PWM rectifier, a new kind of multi-phase rectifying alternating circuit using phase shifting reactor for harmonics elimination is proposed. The selected harmonic components can be reduced or eliminated by selecting correspondent phase-shifting angles. The harmonics repression principle, structrure of phase-shifting reactor, determination of turns and connection mode of the phase-shifting windings etc. are analyzed. The mathematical model of multi-phase rectifying system with phase shifting reactors are built. The simulation and experimental study on a 6-phase and 12-phase rectifying system with phase shifting reactor are carried out. The experimental results show that the multi-phase rectifying system with phase shifting reactor can effectively reduce the current harmonics on the AC power supply side.(3) To meet the requirements of harmonic suppression and self-starting of the high speed generator, a combined converter of inverter with active power filter (APF) is investigated. The APF/inverter works as an inverter during the generator starting and as an APF during the normal AC/DC power conversion. The relation between the capacity of APF and that of the compensation objects is analyzed. The detection method on harmonic current, the control strategy of double closed loop and the special harmonic elimination control technology are studied. The comparative study on harmonic suppression at frequency 1000Hz for different modulation strategies is carried out.(4) Two approaches, a third-order harmonic injection with passive circuit and a sixth-order harmonic injection of a single-switch PWM rectifier, are employed to suppress the dominant harmonic components in the input currents on distributed high speed generator system. Based on their principle analysis, the relevant strategies are investigated and the simulation studies at 1000 Hz are carried out respectively.(5) To satisfy the requirement of different users, a three-phase four-leg circuit topology inverter is investigated to balance output voltage. The transfer functions and system transfer functions matrix are deduced. Three-dimensional space voltage vector modulation strategy is analyzed. The triangular prism judgment, the tetrahedron discrimination and computational methods of space vector action time are discussed. The simulation results verify the feasibility of the proposed design structure and control strategy.(6) A six-phase-shift reactor prototype is developed and tested, which is used for the AC/DC power conversion in the high speed permanent-magnet generator with rated power of 75kW and rated speed of 60000r/min. In addition, an experimental platform is also designed and built based on dual DSP (TMS320LF2407A), the bidirectional PWM converter and 3-phase 4-leg inverter are tested partly based on the platform.