Research Of DSP Based Single Phase Parallel Inverter

Parallel operation of multi-inverters provides a good way to increase the capability and redundant operation, which makes the parallel operation of inverters more and more widely used. In addition, with fast development of digital power converter technique, digital control SPWM inverter has become the main stream of the inverter. Digital control technique and parallel operation technique of inverter have attracted much attention.Single-phase full-bridge inverter and its control method have been studied in this paper. The operation principle of single-phase full-bridge inverter has been analyzed. Open loop characteristics of single-phase full-bridge inverter are given, the mathematical model of SPWM inverter is established and the reasons for the output voltage waveform distortion are researched. Based on which, transfer function of single-phase full-bridge inverter is derived based on double closed-loop control, consisting of outer voltage loop and inner inductor current loop, and characteristics of the closed-loop inverter were studied. Finally, steady state and transient characteristics of double closed-loop controlled single-phase full-bridge inverter are researched by simulation.Based on the analysis of single-phase full-bridge inverter, equivalent model of two inverter parallel system is established. According to the equivalent model, the reasons of circulation current are analyzed and some factors, such as reference voltage, voltage feedback coefficient, output voltage amplitude, which influence circulation current, are discussed. Based on double closed-loop controlled inverter, the parallel operation of multi-inverter is achieved by adding an external current sharing loop. The mathematical model of parallel inverter system is built, then, the stability and voltage regulation ability of the current-sharing controller is analyzed. Based on which, an improved two-loop average current-sharing control scheme is proposed in this paper, and over-current protection can be achieved for double closed-loop controlled inverters which consists of outer voltage loop and inner inductor current loop. Detailed analyses of the average circuit and synchronization circuit with average-current-sharing scheme are achieved.Based on theory analysis, the simulation model of parallel inverter system is established by PSIM, steady state and transient characteristics of the parallel inverter system are analyzed by simulation. Two lkW experimental prototypes are designed which compose the parallel inverter system. Some software modules of digital control system have also been performed such as initialization module, PI algorithm module, soft-start algorithm module and duty cycle saturation module. Simulation and experimental are presented to verify the right of the control scheme and the designed parameters.