Research And Design Of Bidirectional AC-DC-AC Converter For Wind Power Generation

Under the background of global low-carbon concept and domestic "carbon peak" and "carbon neutral" policies,the proportion of green,flexible and efficient wind power generation in China’s energy supply structure has been steadily increased year by year.However,due to the stochasticity of wind energy,the output of wind power generation system is subject to unstable fluctuations,so the output of wind power generation system is usually not directly connected to the AC grid.The bidirectional AC-DC-AC power electronic converter,as the energy transmission link between the AC grid and the wind power generation system,reduces the coupling of the AC network at both ends of the power electronic converter due to the existence of its DC bus.Based on the analysis of the physical structure,commutation process,and control strategy of phase-controlled converters based on semi-controlled power semiconductor devices and PWM converters based on fully-controlled power semiconductor devices,this thesis conducts a simulation experiment comparison of the two types of converters.The conclusion is that the PWM converter is superior to the phase-controlled converter in terms of current harmonic content,DC voltage level,and grid-side power factor at medium power levels.According to the results of the simulation comparison experiment,this thesis uses fast control prototype technology and designs and builds a hardware control system for bidirectional AC-DC-AC PWM converters using fully-controlled semiconductor power devices.The current-carrying capacity,voltage withstand capability,signal transmission delay,and switching frequency of core circuit components such as voltage and current collection and power bridge driving are discussed in detail and quantitatively calculated,and relevant devices are selected and printed circuit boards are developed accordingly based on the calculation results.To ensure the correctness and reliability of the bidirectional AC-DC-AC PWM converter system,this thesis tested the fidelity of the voltage and current sensing components for signal reconstruction,the over-voltage suppression capability of the power bridge buffering circuit for fully controlled power semiconductor devices,and the driving ability of the driving circuit for power switches.The test results showed that the signal acquisition error of the voltage and current sensing components was less than2.5%.The driving circuit could control the power switches to work normally at a frequency of 20 k Hz,and the turn-on and turn-off delays were both less than 1 us,meeting the requirements for real-time and accuracy of the control system.Meanwhile,the power bridge buffering circuit also exhibited a significant suppression effect on the overvoltage during the turn-off process.Finally,based on the bidirectional AC-DC-AC converter hardware control system,using the RT-Lab digital real-time controller and fast control prototype technology,this thesis completes the hardware system verification of the grid-side converter vector control strategy based on space vector modulation and the magnetic field orientation vector control strategy,and performed the feasibility verification on the overall control of the bidirectional AC-DC-AC converter.