Isang Bagong Modular na Solusyon sa Pagsusuri para sa mga Sistemang Photovoltaic at Paghahanda ng Enerhiya

1. Pagkakaroon at Background ng Pagsasaliksik​

​1.1 Kasalukuyang Kalagayan ng Industriya ng Solar​
Bilang isa sa pinakamaraming renewable energy sources, ang pag-unlad at paggamit ng solar energy ay naging sentral sa global na transition ng enerhiya. Sa mga nakaraang taon, dahil sa mga patakaran sa buong mundo, ang industriya ng photovoltaic (PV) ay dumaan sa explosive growth. Ang mga estadistika ay nagpapahiwatig na ang industriya ng PV sa Tsina ay nakamit ang isang nakakabuluhang 168-fold na pagtaas sa panahon ng "12th Five-Year Plan". Nang makarating sa katapusan ng 2015, ang installed PV capacity ay lumampas sa 40,000 MW, na nanalo bilang unang ranggo sa global para sa tatlong sunod-sunod na taon, na inaasahan pa ring magpatuloy ang paglago sa hinaharap.

​1.2 Umiral na Problema at Teknikal na Hamon​
Bagama't may mabilis na pag-unlad, ang mga tradisyonal na PV energy storage systems ay patuloy na nakakaharap sa maraming teknikal na bottleneck sa praktikal na aplikasyon:

• ​Mga Isyu sa PV Array:​​ Upang matugunan ang load voltage at power requirements, karaniwang konektado sa serye at parallel ang malaking bilang ng individual na PV cells. Ang struktura na ito ay masusuka sa partial shading, na nagdudulot ng "mismatch" losses at hot-spot effects, na siyang nagbabawas ng system power generation efficiency at seguridad.
• ​Mga Isyu sa Energy Storage Battery Pack:​​ Ang battery packs, na gumagamit din ng serye-parallel configurations, ay may inherent na balancing problems. Ang battery inconsistency ay lumalala habang tumaas ang scale, hindi lamang nagdudulot ng pagtaas ng system complexity kundi nagdudulot rin ng pagbaba ng capacity at maikling lifespan, na nagiging hadlang sa large-scale application.
• ​Kakaunti ng Umiiral na Teknolohiya:​​ Bagama't may ilang mga mananaliksik na nagpropose ng passive equalization management techniques, ang mga pamamaraan na ito ay simpleng inilipat ang balancing problem nang walang full consideration sa impact ng multi-module series connection sa downstream circuits. Kaya sila ay kulang sa scientific guidance sa pagpili ng key components tulad ng PV cells.

​II. Buong System Solution at Topology​

Ang core ng solusyon na ito ay ang pagbuo ng bagong, modular, at scalable power system topology.

​2.1 Hierarchical System Composition​
Ang sistema ay estrukturado hierarchically mula sa basic unit pataas sa tatlong levels:

1. ​Module (Basic Unit):​​
• ​Composition:​​ Isang single PV cell, isang single storage battery (na may matched voltage at capacity), 4 power switches, at independent controller.
• ​Function:​​ Bilang ang pinakamaliit na autonomous unit, ang controller ay nagmamanage ng 4 switches upang mag-enable ng independent connection/disconnection ng PV cell at battery, na nagbibigay ng flexible switching sa limang operating modes.
2. ​Series String:​​
• ​Composition:​​ Nabuo sa pamamagitan ng koneksyon ng ilang modules sa serye.
• ​Function:​​ Nagdudulot ng pagtaas ng total output voltage ng string upang tugunan ang input voltage range ng downstream DC/DC boost converter.
3. ​System:​​
• ​Composition:​​ Nabuo sa pamamagitan ng koneksyon ng maraming series strings sa parallel, na nag-converge sa pamamagitan ng DC/DC converter sa common DC bus.
• ​Function:​​ Ang DC bus ay maaaring direktang magbigay ng power sa DC loads o, sa pamamagitan ng DC/AC inverter, magbigay ng power sa AC loads.

​2.2 Core Advantages​
Ang topology na ito, sa pamamagitan ng individual cell-level independent control, ay fundamental na nagwawasak sa inherent shading effects at battery balancing issues ng traditional series structures sa physical level. Sa tamang pagpili ng component, ang sistema ay nagpapahintulot sa PV cells na laging operasyon sa kanilang Maximum Power Point (MPP), na nagreresulta sa pag-alis ng pangangailangan para sa additional MPPT circuits at complex Battery Management Systems (BMS).

​III. Hierarchical Monitoring Strategy​

Ang solusyon na ito ay gumagamit ng hierarchical control strategy upang makamit ang refined monitoring mula sa local hanggang sa global levels.

​3.1 Module-Level Monitoring Strategy (Autonomous Control)​​
Bawat module ay autonomously nag-switch sa mga sumusunod na 5 operating modes batay sa sariling status (PV output voltage, battery voltage):

​3.2 String-Level Monitoring Strategy (Voltage Coordination Control)​​
String-level monitoring uses the DC/DC converter's input voltage (U_in) as the key parameter, stabilizing voltage by connecting/disconnecting modules.

• ​Control Objective:​​ Ensure U_in remains within the DC/DC circuit's allowable operating range (e.g., 12V ~ 22V).
• ​Threshold Control Logic (e.g., for 24V system):​​
• ​Low Voltage Threshold (16V):​​ If U_in < 16V, the monitoring system automatically searches for modules within the string that are in standby mode but have normal battery charge, commanding them to connect, preventing the DC/DC from shutting down due to low input voltage.
• ​High Voltage Threshold (20V):​​ If U_in > 20V, the connection of new modules is restricted to ensure U_in does not exceed the DC/DC's maximum input voltage.
• ​Protection Threshold (12V):​​ If U_in < 12V, the string is deemed depleted, forcibly disconnecting it. All modules enter standby mode until a sufficient number of batteries recover charge.

​3.3 System-Level Monitoring Strategy (Global Protection)​​
System-level monitoring focuses on ensuring power supply quality, with the DC bus voltage (U_bus) as the key monitoring point.

• ​Control Logic:​​ The DC bus voltage is monitored in real-time. If the voltage falls below a critical threshold (e.g., 80% of 24V system rating, i.e., 22V), it indicates insufficient total system energy. The monitoring system will execute a global shutdown command to protect the inverter and load equipment, ensuring AC-side power quality.

​IV. Key Component Selection Method​

To address the matching problem between PV cells and storage batteries, this solution proposes a selection method aimed at maximizing solar energy utilization efficiency.

• ​Core Idea:​​ In this system, the operating voltage of the PV cell is clamped by the battery voltage, making the matching of their voltage parameters critical.
• ​Selection Model:​​ Based on an engineering mathematical model of the PV cell (considering temperature and irradiance effects), the system efficiency η is derived as a function of the battery voltage U_BAT and the PV cell's maximum power point voltage U_mp.
• ​Conclusion:​​ For a 3.7V storage battery with an operating voltage around 3.9V~4.0V, simulation results indicate that the system's solar energy utilization efficiency is highest when the PV cell's U_mp is approximately 4.25V. Therefore, in practical selection, the PV cell's U_mp should be controlled within the range of 4.2V ~ 4.3V.

​V. Expected Outcomes​

1. ​Significant Efficiency Improvement:​​ Modular independent operation completely eliminates the inherent "bucket-brigade effect" and hot-spot issues of series structures, ensuring each unit operates efficiently. Simultaneously, precise voltage matching between PV and storage enables approximate Maximum Power Point Tracking (MPPT) without additional circuits, greatly enhancing power generation efficiency.
2. ​Enhanced Lifespan and Reliability:​​ The modular structure fundamentally resolves the balancing challenges caused by battery pack inconsistencies, avoiding overcharging and over-discharging, effectively extending the overall system lifespan. The hierarchical monitoring strategy provides multiple layers of protection from local to global levels, significantly improving system robustness.
3. ​Cost Optimization and Convenient O&M:​​ This design successfully eliminates the need for complex MPPT trackers and Battery Management Systems (BMS), reducing hardware costs. Its "Lego-like" architecture makes installation, maintenance, and expansion extremely convenient. Failure of a single module does not affect overall operation, reducing the total lifecycle cost.