Sub-module differential power processing for photovoltaic applications

Photovoltaic;solar;differential power processing;maximum power point tracking

Qin, Shibin ; Pilawa-Podgurski ; Robert C.

关键词: Photovoltaic;    solar;    differential power processing;    maximum power point tracking;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/49501/Shibin_Qin.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Photovoltaic energy offers great benefits over conventional energy resources, but its large scale deployment has long been hindered by the prohibitive cost and low energy output. Advanced power electronics design plays a critical role in reducing the cost of PV energy systems and improving the power output. Conventional distributed power electronics solutions in a PV system such as DC optimizer and micro-inverters have been developed, but still they still have certain limitations in terms of cost and efficiency. This thesis proposes the use of a technique known as differential power processing (DPP) to achieve substantial efficiency improvement and cost reduction over the conventional solutions and develops hardware and control design to apply the DPP technique to a PV system. This thesis introduces the fundamental principle of differential power processing and highlights its advantages over the conventional solutions. Several hardware designs of the DPP converter are presented, and several prototypes have been built and tested. These hardware prototypes achieve high conversion efficiency and very small volume to the point that they can be easily fit into a PV module junction box (commonly referred to as PV module integration). Moreover, a distributed algorithm for controlling DPP converters in a PV system is developed. This algorithm achieves true maximum power point tracking (MPPT) of series-connected PV sub-modules by relying only on local voltage measurements and neighbor-to-neighbor communication between the DPP converters. Compared to previous solutions, the proposed algorithm achieves a reduced number of perturbations at each step and potentially faster tracking without adding extra hardware; all these features make this algorithm well-suited for long sub-module strings. An indoor experimental setup was established and various experiments prove the effectiveness of the proposed algorithm. Finally, the DPP technique is applied to a micro-inverter system. Micro-inverters typically perform only module level MPPT and do not address power losses due to uncompensated sub-module mismatch. The thesis provides a solution to seamlessly integrate DPP converters into the existing micro-inverter system to improve its energy capture by recovering power losses due to sub-module mismatch.To demonstrate the effectiveness of the proposed solution, a hardware prototype was built and tested with an off-the-shelf commercial micro-inverter to prove the concept. The improvement in energy capture with DPP converters is experimentally verified.