Three Level DC-to-AC Power Inverter for Power Grid Operation

Abstract:- In case of medium voltage (several tens up to hundred volts on DC-side) solar inverter applications a DC-to-DC converter for voltage level adaptation is required in front of the DC-to-AC inverter. This leads to a two-stage concept with accumulation of the losses. In our case a concept was chosen, where the efficiency in each stage is maximized by usage of the best-fit topology. Conventional power inverters used in mains connected applications fight with the disadvantage of the hard switched PWM power stage operating at high voltages [1,2]. Also soft switching topologies [6,7] do not give full benefits at all. In this paper the conjunction of simple boost- and buck converter stages gives the facility to realize an optimal design for power grid coupled inverters. The reduced voltage stress of each stage can lead to a significant improvement of the system losses. Furthermore it is shown, that a revised method of energy storage in the ‘weak ’ DC-link can be used for smoothing the input current. Sharing of the energy flow in each power stage can also lead to reduced losses. The topology presented here shows a remarkable improvement of the switching losses and significantly reduced electromagnetic compatibility (EMC)