Maximum Power Point Tracking Control For Grid-connected Photovoltaic Systems

As greenhouse effect and environment pollutions are getting worse dueto over-using fossil fuels, the global energy problem has caused more andmore people’s attention. The demand of clean energy is increasingtremendously, which stimulates the study of electrical power generationsystem. Solar energy, as one of the clean electrical power energy, has beengreatly focused due to its renewable and abundant resources.Although solar energy has been paid a lot of interests and many resultsare obtained, the energy convert efficiency is still low and is an open issue inthis area, where the Maximum Power Point Tracking (MPPT) method is akey technology to improve the efficiency in photovoltaic grid-connectedgeneration systems. By regulating the output voltage or current of thephotovoltaic array, the photovoltaic system could keep working on themaximum power point despite of dramatic changes of light intensity ortemperature. Due to the nonlinear characteristics of photovoltaic array, the opencircuit voltage and short circuit current, which are largely influenced by lightintensity and temperature, will have direct effects on its maximum power.Variation of the natural conditions will also lead to the correspondingchanges in output characteristics and maximum power point. Therefore, if thesystem will always work on its maximum power point, the efficiency of thesolar energy conversion will be inevitably high.Second, the conversion efficiency of photovoltaic array in our daily lifeis not high enough and the price of the materials is very expensive. What’smore, in the practical application, the natural light intensity and atmospherictransmittance are dynamic and difficult to keep as a constant in our real world.When the partial shaded conditions occurred, the global maximum powerpoint should be considered, we use SVM method to build power method todefine the control objective.Finally, connected-grid MPPT method for the Cascaded H-Bridge isderived by minimizing the power quality and maximizing conversionefficiency. Simulation illustrates that the control scheme is capable ofcontrolling the dc-link current to the desired MPPT reference current, whileinjecting sinusoidal current to grid with reduced total harmonic distortion.Accuracy of the model, reducing of the switching frequency and Total Harmonic Distortion of the sinusoidal current injected to the grid. Further, thepartial shading of photovoltaic arrays has been a hot topic in the MPPTproblem, research on MPPT method under this circumstance and theinfluence of the grid side will be an interesting work.