The Study On DSP Controlled Three Phase Inverter For Redundant Parallel

As the requirement of high quality and reliability power supply increasing, Uninterruptible power system (UPS) are widely used. And the UPS module working in parallel which can expand capacity and realize redundancy in power supply system, increase the capability and reliability of power system .So they are now considered as one of the most important part in the field of inverter technology.This thesis is mainly devoted to the analysis of circulating current's characteristics and the control technologies of parallel inverter system without output isolating transformers. In this thesis the inverter control method is dual loop on voltage and inductor-current feedback with an outer average voltage loop. Base on the inverter model, The expression of equivalent output impedance is deduced and the models based on equivalent output impedance for double close-loop controlled inverter and its parallel system are also established. Based on the analysis of circulating current characteristics of parallel inverter system, an improved parallel control strategy based on real and reactive power is presented, which including the reference voltage phase and amplitude adjusts, power calculation and output voltage synchronized in different inverter. Additionally, the reasons of DC bias contained in the output voltage of double close-loop controlled inverter are discussed, and the methods for detecting and digital adjusting DC bias with high precision are also analyzed, and the reasons and methods for detecting and restraining DC circulating current in parallel system based on double close-loop controlled inverters are also studied. In the end the experimental results prove that the methods mentioned above have good performance on Redundant parallel system .