Research On Hybrid Control Strategy For Single-phase UPS Inverters

Constant Voltage Constant Frequency (CVCF) SPWM Inverter is the core of the whole Uninterruptible Power System (UPS). With the rapid development of information technology, the output performances and reliability of inverters are becoming more and more important. To achieve an output voltage with low Total Harmonic Distortion (THD), high stability and fast transient response in various load condition, many waveform correction technologies have been proposed.Assuming the load is resistive or taking the current of load as a disturbance input, continuous state-space model and discrete state-space model of inverter are established. It is analyzed that causing the waveform distortion including dead-time effect and load disturbing. Essentiality of the waveform correction technology is pointed out. A co-simulation platform is built with the help of MATLAB/Simulink and Saber software, and the platform is the base of farther analysis and simulation.Repetitive control technology is arising from the internal model principle. It's a compensate control technology based on period time. It can entirety eliminate the distortion of waveform. For the limitation of itself, repetitive control cannot get well transient response. This thesis presents a theoretical analysis and a systematic research on the repetitive control scheme. The parameter design method of the repetitive controller is introduced. System stability, steady-state error and error convergence of the repetitive controller system are specially disused, and a sufficient condition for stability is presented.A novel hybrid control strategy based on fuzzy control and repetitive control is proposed. Fuzzy logic controller can improve the dynamic performance of the system and repetitive controller can ensure the steady-state performance of the system. Thus, the two control strategies can coordinate with each other so that the inverter can produce high quality voltage waveform and has a fast transient response. The simulation results show that the proposed hybrid control strategy is feasible and effective.