Abstract
Series–parallel module technology can meet a DC converter’s requirements of high-power, large-capacity, and high step-up ratio in photovoltaic a DC boost collection system. However, the cascaded structure has the problem of voltage and current sharing between modules, and due to the duty cycle limitation of converters, the combined converters in the PV-converter unit have an unbalanced voltage, which may also exceed the voltage range under partial shading conditions (PSCs). First, aiming at the problems of voltage sharing, current sharing, and low modularity in the combined converter, this paper proposes a distributed control strategy. Then, by adopting a coordinated control strategy based on the sub-module cutting in and out, the problem that the combined converter cannot normally boost under PSCs was solved. The paper not only takes the advantages of the cascade structure of the combined converter to increase the power and voltage, but also improves its modularity to solve the problem of abnormal operation under uneven irradiation. This dramatically improves the adaptability of combined converters in a photovoltaic DC collection system. Finally, a small power experiment was carried out, where the experimental results verified the effectiveness of the control strategy.
Highlights
Due to the increasing scale of photovoltaic plants, the problems of harmonic resonance and reactive power transmission in the traditional AC collection system are becoming increasingly prominent.It will harm the operation of photovoltaic power plants and power systems, and seriously affect the transmission capacity of photovoltaic power plants [1,2,3]
A high-power, large-capacity, high-ratio DC converter is the key equipment for the DC boost collection of large-scale photovoltaic power plants
Each is boosted by by the combination converter and connected series,and andafter afterphotovoltaic reaching the the array high voltage direct the combination converter connected ininseries, reaching high the combination converter and connected in series, and after reaching the high voltage direct current (HVDC) transmission level, it is connected to the grid using long-distance DC transmission
Summary
Due to the increasing scale of photovoltaic plants, the problems of harmonic resonance and reactive power transmission in the traditional AC collection system are becoming increasingly prominent. Gowaid et al [15] proposed an auto-coupling DC transformer topology, which reduces the loss of the two-stage structure but increases the complexity of the system control Both high-voltage switching technology and multi-level converter technology have some disadvantages that limit their application in the field of high-voltage DC conversion. The modular series–parallel technology uses a modular structure to form a combined converter, which can reduce the voltage level of the device, and realize a power expansion It has better application prospects in the photovoltaic (PV) DC collection. This study adopted a combination converter with an input parallel output series (IPOS) structure; the input with a parallel connection is beneficial to improve the power and boost ratio of the converter, while the output with a series connection helps to increase the DC collection voltage level. Conclusions and contributions of the paper are drawn in the last section
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