Efficiency analysis of an isolated series resonant buck-boost chopper inverter

As the demand of renewable energy increases, distributed generator (DG) systems are widely used as a necessary supplement to the central power generation. In order to effectively utilize the electrical power from the DG, a power conversion stage needs to be introduced to convert the electrical power to suit various loads.; The power inverter, which is responsible for converting the energy from DC to AC, plays a vital role in DG systems. Maintaining high inverter efficiency has become one of the main issues in power electronics research.; Because of the better performance in efficiency, one or two stage inverters having fewer switches, high frequency (HF) transformer and soft-switching structures are becoming the main stream of inverter designs for the future. Based on these considerations, the isolated series resonant buck-boost chopper inverter with mixed parallel mode (MPM) is proposed in this thesis for medium power applications to achieve the high efficiency.; In order to eliminate the tail current loss of the insulated gate bipolar transistor (IGBT), MPM is selected. Different from using a single IGBT or metal-oxide semiconductor field effect transistor (MOSFET), MPM has the advantages of reducing the turn-off losses of the IGBT compared with the single IGBT mode and maintaining lower conduction losses compared with the single MOSFET mode.; The relationship between the output voltage and the duty ratio suggests that instantaneous voltage feedback control (IVFC) has to be implemented to make the system stable. In addition to that, a channel selection switch (CSS) technique is also proposed to implement the MPM operation.; The efficiency analysis and comparison between different switching modes based on the same topology are given. Generally speaking, the high efficiency operation can be achieved based on the isolated series resonant buck-boost chopper inverter under different switching modes. In those medium and high power applications, MPM works very well in reducing the tail loss of the IGBT. However, in low power applications, the single MOSFET mode has better efficiencies compared with the MPM. A trade-off power line between the MPM and the single MOSFET mode is discussed in detail. It is also verified that the trade-off line increases as the input voltage goes up.; The hardware prototype shows that the proposed topology is working properly under the single IGBT mode. The experimental results also prove and support the theoretical analysis and simulation.; The efficiency analysis provides a guideline to choose the different switching modes wisely based on the same topology. It also indicates that the isolated series resonant buck-boost chopper inverter with the MPM operation has the flexibility in both high power and low power applications; at the same time, high efficiency operation and stable performance can be achieved. It is expected that the proposed topology with the MPM operation will be widely implemented in medium power DG systems in the future.