Dual DC-DC converter design for string inverters used in solar plants

This study deals with the design of a dual buck converter where both of them are simultaneously operated to regulate photovoltaic (PV) string inputs. The proposed control and converter structure is intended to improve the dc-bus interface for solar arrays and to control the dc bus voltage of a commercial grid-tie inverter that is generated by four PV arrays. The control algorithm is improved by including PI control to the regular perturb-and-observe algorithm. Regarding to the international standards on single-phase commercial string inverters such as AS4777-2013, IEC62109, and IEC61727, the maximum power of each solar array is allowed to be 1.2 kWp while the maximum total input power is limited to 4.8 kWp. Individual MPPT controllers that are improved in this study control each one of the dc converters handling dual solar arrays at the input connection. The dc interface voltages regulated by converters are coupled on a unique dc bus to generate the supply voltage of inverter section. The controllers perform a robust operation against the freely fluctuating irradiation values of each solar arrays.