Distributed autonomous voltage balancing control for a modular IPOS DC grid-connected renewable power system

Analysis and Control of Input-Parallel Output-Series Based Combined DC/DC Converter With Modified Connection in Output Filter Circuit

“…From (13) and 14, it can be concluded that the voltage balance performance is affected by the output filter capacitors (C f1 and C f2 ), ESR of capacitor (R c1 and R c2 ) and voltage balance resistor (R b1 and R b2 ) in the case without connection of point O and point M. While as shown in (15) and (16), if the point O and point M are connected together, the transformer resonant inductor and duty cycle loss (indicated by R d1 and R d2 ) also have influence on the voltage deviation between u o1 and u o2 . Ideally, if there are no parameter deviations, (14) and (15) will always be zero, that indicates voltage balance can be completely realized both in dynamic and steady states. Using the parameter values listed in Table 2, deviations are assumed for different parameters to evaluate the voltage balance performance of the capacitor voltages, u o1 and u o2 in this section.…”

“…Furthermore, if point O and point M are connected in Fig. 7, then the voltage deviation betweenũ o1 andũ o2 can be evaluated by (15) according to circuit theory.…”

“…Generally, in such a conversion system, the voltage value of power source is relatively low, while the output of the converter is interfaced to a high voltage DC bus, therefore, if there is only one DC/DC module is adopted, the input current of converter is large that will lead high current stress on the input side power switches, while the power switches in the output side have to tolerate high voltage stress. The IPOS converter usually consists of multiple DC/DC converter modules of lower rating, and the DC/DC converter modules can be either non-isolated [8]- [10] (e.g., using Boost and bidirectional converter) or isolated topologies [11]- [15] (e.g., using PSFB and dual active bridge). Since the large input current is shared by the input-parallel configuration, the conduction losses of power switches can be reduced which is conducive to improve power conversion efficiency [16].…”

Fault analysis on DC transmission system of PV generation

“…Due to the low output voltage of a single PV array, m input‐parallel output‐series connected isolated boost full‐bridge converters are adopted to boost the DC voltage and reduce the transmission loss. Small‐capacity DC/DC converters in series can reduce the manufacturing difficulty and the voltage stress of the submodule, while the voltage sharing and power allocation problems have been basically addressed . In order to obtain satisfied power quality, as well as to improve the system control flexibility and reduce the number of DC circuit breakers, the CDSM‐MMC with DC fault isolation capability is adopted as the grid‐connection inverter.…”