A study on steady characters of inverter interfaced distributed generation in three phase symmetrical system

Recently inverters are all-pervading used as the connective instrument of distributed generations and distributed power system. When inverter interfaced distributed generations are connected to the distribution system, it may bring some new problems on load flow and fault characteristic and protection. The analysis on steady characters of PQ control mode and VF control mode inverter interfaced distributed generation is done when the system is three phase symmetrical. Generally speaking there are limits on power and current in control system for the security of distributed generations and power electronic devices in inverter, so the analysis is more complex. The mathematical analysis on three phase symmetrical system is done and restriction equations are described whether three phase symmetrical fault occurs or not. For the solution of the equation groups expresses the steady state of the system, so the solution of the equation groups is one and only. Then the restriction equation groups are solved. The solution in different areas shows the reason of steady non-linear character of inverter interfaced distributed generations and the simulation shows the conclusion correct. The steady characteristic curves of PQ control mode and VF control mode inverter interfaced distributed generation about voltage and current and power are got from the function of voltage and current and power at the same time. PQ control mode and VF control mode inverter interfaced distributed generation behave similarly but not identically when three phase symmetrical fault occurs in three phase symmetrical system. The disadvantageous influence on protection is analysed by the way.