Study On Control Technology For Parallel Inverters

Power converter modules working in parallel state is a new way to expand supply system capacity and it is one of the vital regions in power electronics. Each parallel module takes its share of the load, so the current stress for power switch reduced greatly. Higher reliablility, lower cost and higher power density can be achieved by this way for large capacity power system and also system configuration becomes more flexible.On the basis of deep analysis of parallel operation theories and technology, a parallel operation analysis of parallel system about modular inverter is designed for engineering practical project application. Soft switch technology and DSP (Digital Signal Processor) will be adopted in this system especially.First, the paper analyzes the principle of parallel inverter system and develops mathematical models about it. Based on it after several modes are proposed including sharing current control, parallel control strategy and characters of loop-current, a reliable solution of restraining loop-current is designed. As to some disadvantage of traditional transformer of city frenquency and some typical DC/DC (Direct Current/Direct Current) mode, two phase control pattern of DC/DC and DC/AC is adopted. In the dissertation DC/DC circuit of half bridge has some characters of soft switch and current loop measure.Integrated control strategy, which combines the control theory of SPWM and high-powered DSP, is designed including single polarity double frenquency SPWM, close loop of instantaneous voltage, and intelligent PI adjuster in order to accomplish DC/AC conversion. On the second thoughts it avoids some shortcoming of complicated analog PI adjuster. In the system we set up double safeguard of soft programme and hardware to advance the dependability of the inverters. Afer the theory of tracking phase is analyzed, this control style, in which there are no fixed master-slave modules and no synchronal signal wire, makes those parallel inverters of system synchronal well, and synchronizes the inverters and the city electricity.A novel parallel operation system based on CAN and DSP, which is used by load sharing and synchronization controlling, is proposed in this dissertation. Auxiliary power source is designed in the chip of UC3846. This dissertation also works into EMC in relation to the design of a real system.