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Distributed MPPT Improves Efficiency of Solar Photovoltaic Systems
- May 23, 2018 -

Describes the problem of reduced power generation due to the obscuration of some panels in solar photovoltaic systems, and the advantages of the distributed maximum power point tracking system (MPPT) at the panel level, as well as various case studies using SolarMagic technology. It was discussed.

Solar energy is one of the most promising renewable energy sources on the market. As the government introduced incentive policies and the rising cost of traditional electricity, more and more families began to switch to solar energy and installed photovoltaic (PV) systems on the roof. According to current PV system price calculation, users usually get return on investment after 7-8 years. The government incentives and the lifetime of the PV system must last for 20 years or more. The return on investment of solar PV systems depends on the annual power generation of the system. Therefore, the photovoltaic systems required by users must be highly efficient, reliable, and easy to maintain, so as to obtain maximum power generation.

Nowadays, many users who install solar photovoltaic systems have realized that partial or intermittent shading will affect the power generation of the system.

Partially shadowed effects on solar photovoltaic systems:

When trees, chimneys, or other objects cast shadows that cover the photovoltaic system, the system causes a "mismatch" problem. Even if the PV system is only shaded by a little shadow, it will cause a significant drop in power generation. The actual impact of partial out-of-pair power generation caused by partial obscuration is difficult to obtain by a simple calculation formula. There are many factors that affect the system's power generation, including the interconnection between internal battery modules, module orientation, serial and parallel problems between photovoltaic cells, and the configuration of inverters. Photovoltaic modules are interconnected by a plurality of battery strings, each battery string being referred to as a "group column." Each bank is protected by a bypass diode to prevent one or more batteries from being obscured or damaged resulting in damage to the entire battery string due to overheating. These series or parallel battery strings enable the panel to generate a relatively high voltage or current.

Photovoltaic arrays are made of parallel connected photovoltaic modules connected in parallel. The maximum voltage of each PV module must be lower than the maximum input voltage rating of the inverter.

When the photovoltaic system is partially shielded, the current in the unshielded battery flows through the bypass diode of the shielded portion.

When the PV array is obscured and this occurs, a V-P electrical curve with multiple peaks is generated. Figure 1 shows a standard grid-tied configuration with centralized Maximum Power Point Tracking System (MPPT) functionality, where two panels in a group are shaded. The centralized MPPT cannot set the DC voltage, so the output power of both groups cannot be maximized. At the high DC voltage point (M1), MPPT maximizes the output power of the unmasked group. At the low DC voltage point (M2), the MPPT will maximize the output power of the mask group: the bypass diode bypasses the shield panel and the unshielded panel in this array will provide the full amount of current. Multiple MPPs of the array may result in an additional loss of the centralized maximum power point tracking (MPPT) configuration because the maximum power point tracker may get the error information to stop at the local maximum point and stabilize with the secondary advantage of having V-P characteristics.

Minimize system mismatch with distributed MPPT:

In order to maximize the power output of each solar panel in the array, National Semiconductor developed SolarMagicTM technology. With this technology, each panel can still output the maximum power even if there are mismatch problems with other panels in the array. SolarMagic technology uses advanced algorithms and advanced mixed-signal technology to monitor and optimize the production of each solar panel, thus compensating up to 50% of the power loss due to mismatch problems. SolarMagic Power Optimizer can be quickly and easily installed in traditional solar PV systems.

The system has two group columns formed by n modules connected in parallel. For the sake of demonstration, each group column in the figure shows only 3 photovoltaic modules, but the group column is usually composed of 5 to 12 modules in parallel to obtain 500-800V. Group voltage.

All modules of group A have no illumination offset problems, and each module has the same characteristics and uniform illumination.

All modules of group B have different characteristics or illumination misalignments due to obscuring, tilting or tilting or collecting more dust. The output of each module is connected at the input of the SolarMagicTM Optimizer (SMO) module. The output of each SMO uses the same series connection as the Group A module.

The SolarMagicTM optimizer module features an efficient integrated power supply circuit that uses a maximum power point algorithm that maximizes the output power of each photovoltaic module. Therefore, the entire group of columns has the same output current, which greatly reduces the hot spot problem and adopts an internal bypass mode. Each SMO module will regulate its output voltage to comply with the overall bus voltage.

The result is that the entire PV system will exhibit an I-V curve with a single maximum power point, simplifying the operation of the central inverter and minimizing the loss of power generated by the mismatch.