Study On Double-Frequency Grid-Connected Inverter Based On Sliding Mode Control And Its Function Expansion

With the emergence of the world’s energy crisis and environmental pollution isworsening, people began to turn their attention to the use of renewable energy. It is ofstrategic importance and value that the renewable energy distributed generationtechnologies with solar and wind power as the representative in achieving the globalenergy conservation and sustainable development of human society. In this context, itbecome a hot spot on that the study focus on the topology and control strategy ofgrid-connected inverter which is the interface device and key equipment to improve theconversion efficiency and output power quality.It can improve the output performance of the system and increase system powerdensity for electronic power converter by increasing the switching frequency. Therefore,it is a trend to improve the switching frequency for the development of the powerconverter. However, the high switching frequency will led to the switching lossesincrease and reduce efficiency of the system. In recent years, some scholars haveproposed the concept of double-frequency converter (DFC) to solve this issue. In theory,the sliding mode control (SMC) requires infinite switching frequency to ensure that thesystem have fully adaptive. The operating frequency of the power electronic devices islimited in the reality, but in order to maintain quasi-sliding mode the switchingfrequency as high as possible is needed. Therefore, the application of SMC for powerconverter exist the problem of excessive switching losses. It can be well combined withthe advantages of SMC and double-frequency grid-connected inverter (DFGCI), that theDFGCI using SMC to ensure a strong robustness to improve system efficiency. At thesame time, the number of grid-connected inverter has increased continuously, andpeople pay more attention to the problem of harmonic pollution. The grid-connectedinverters not only convey power to the grid but also suppress harmonic, which will playa good role in the improvement of power quality.In this paper, the double-frequency grid-connected inverter and its sliding modecontrol is studied in order to obtain good dynamic and static performance. On this basis,the functional multiplexing is also studied.Firstly, the basic principles of double-frequency converter and sliding mode controlare the detailed analysis and presentation. On the basis of the understanding ofdouble-frequency grid inverter principle, the sliding mode control of single-phase double-frequency grid-connected inverter is studied and simulated.Subsequently, the three-phase double-frequency grid-connected inverter isintroduced.Its mathematical model is established. and its sliding mode control isstudied and simulated. Then, the harmonic suppression function of the three-phasedouble-frequency grid-connected inverter is also studied and simulated.Then, a novel three-phase double-frequency grid-connected inverter is proposed toreduce the number of power switches and its work model is analyzed. And the slidingmode control and unified control of the novel topology has been studied and simulated.Finally, the experimental hardware circuit of single-phase double-frequencygrid-connected inverter and its sliding mode control was designed in order to furtherunderstand the working principle of double-frequency grid-connected inverter andverify its feasibility. And the experimental prototype was debugged and testedpreliminary and some experimental results were obtained.