Two-Switch Voltage Equalizer Using an LLC Resonant Inverter and Voltage Multiplier for Partially Shaded Series-Connected Photovoltaic Modules
Various kinds of differential power processing converters and voltage equalizers have been proposed for series connected photovoltaic (PV)modules to prevent negative influences of partial shading, such as significant reduction in power generation and the occurrence of multiple maximum power points (MPPs), including local and global MPPs, that hinders and confuses MPP tracking algorithms to operate properly. However, since conventional topologies are based on multiple individual dc–dc converters, the required switch count increases proportionally to the number of modules connected in series, increasing the complexity. A two-switch voltage equalizer using an LLC resonant inverter and voltage multiplier is proposed in this paper. The circuitry can be dramatically simplified compared with conventional topologies due to the two-switch configuration. Detailed operation analyses for the LLC resonant inverter and voltage multiplier are separately performed.
The existence of multiple MPPs confuses and hinders the conventional MPP tracking (MPPT) algorithm to extract maximum power. Although advanced MPPT algorithms have been proposed, with which a global MPP can be found by sweeping operation voltage over a wide range and tracked even under partially shaded conditions, a significant reduction in power generation due to the bypassed shaded modules is inevitable.
In this project, a two-switch voltage equalizer using an LLC resonant inverter and voltage multiplier is proposed for partially shaded series-connected PV modules. The two-switch configuration can significantly simplify the circuitry compared with conventional topologies of DPP converters and voltage equalizers requiring multiple switches proportional to the number of PV modules connected in series. With the proposed voltage equalizer, local MPPs successfully disappeared, and extractable maximum powers significantly increased compared with those without equalization.
TOOLS AND SOFTWARE USED:
- MP LAB
Masatoshi Uno, Member, IEEE, and Akio Kukita, “Two-Switch Voltage Equalizer Using an LLC Resonant Inverter and Voltage Multiplier for Partially Shaded Series-Connected Photovoltaic Modules”, IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 51, NO. 2, MARCH/APRIL 2015