Isang Bagong Modular na Solusyon sa Paghahamon para sa mga Sistema ng Pagbuhat ng Kapangyarihan sa Photovoltaic at Imprastraktura ng Pagsimpan ng Enerhiya

1. Pagpakilala ug Background sa Pananaliksik​

​1.1 Kasamtangan nga Kahimtang sa Industriya sa Solar​
Isip usa ka sa labi abundant nga renewable energy, ang pagpalambo ug paggamit sa solar energy naging sentral sa global nga transition sa energy. Sa katapusan nga mga tuig, gihatagan sa mga patakaran sa tibuok kalibutan, ang photovoltaic (PV) industry namihasik nga pagkamata. Ang estadistika nagpakita nga ang PV industry sa Tsina nakakita og 168-fold nga pagtaas sa "12th Five-Year Plan" period. Hangtod sa katapusan sa 2015, ang installed PV capacity gibabaw sa 40,000 MW, naging unom sa mundo sa tulo ka sunod-sunod nga tuig, ug inaasahan ang pagpatuloy sa pagkamata sa hinayana.

​1.2 Nalabay ug Teknikal nga Hamubo​
Bagama may rapiadong pag-unlad, ang tradisyonal nga PV energy storage systems sulod pa gihapon sa daghang teknikal nga bottlenecks sa praktikal nga aplikasyon:

• ​PV Array Issues:​​ Aron mapugos ang load voltage ug power requirements, karon gi-connect sa series ug parallel ang dako nga bilang sa individual nga PV cells. Kini nga struktura masusog sa partial shading, resulta ang "mismatch" losses ug hot-spot effects, nga makapahinabang sa sistema nga mawasay ug ma-unsafe.
• ​Energy Storage Battery Pack Issues:​​ Ang battery packs, gamiton usab ang series-parallel configurations, adunay inherent nga balancing problems. Ang inconsistency sa battery mas magbaba kon madaghan, wala lang nagdugay sa system complexity apan nagdugay usab sa capacity degradation ug shortened lifespan, nahimong pipila sa large-scale application.
• ​Insufficiencies sa Existing Technologies:​​ Bagama gitumong niadtong pipila ka researchers ang passive equalization management techniques, kini nga mga paraan ra nag-shift sa balancing problem wala gyud fully consider ang impact sa multi-module series connection sa downstream circuits. Wala usab sila scientific guidance sa pagpili sa key components sama sa PV cells.

​II. Overall System Solution ug Topology​

Ang core niining solusyon mao ang pagconstruct og bag-ong, modular, ug scalable power system topology.

​2.1 Hierarchical System Composition​
Ang sistema gi-strukturado hierarchical gikan sa basic unit hangtod sa tulo ka levels:

1. ​Module (Basic Unit):​​
• ​Composition:​​ Usa ka single PV cell, usa ka single storage battery (with matched voltage ug capacity), 4 power switches, ug independent controller.
• ​Function:​​ Isip ang pinakagamay nga autonomous unit, ang controller manages ang 4 switches aron mahimo ang independent connection/disconnection sa PV cell ug battery, allowing flexible switching sa lima ka operating modes.
2. ​Series String:​​
• ​Composition:​​ Giformed pinaagi sa pagconnect sa pipila ka modules sa series.
• ​Function:​​ Nag-increase sa total output voltage sa string aron match sa input voltage range sa downstream DC/DC boost converter.
3. ​System:​​
• ​Composition:​​ Giformed pinaagi sa pagconnect sa multiple series strings sa parallel, converging pinaagi sa DC/DC converter sa common DC bus.
• ​Function:​​ Ang DC bus makapagtubag direct sa DC loads o, pinaagi sa DC/AC inverter, makapagtubag sa AC loads.

​2.2 Core Advantages​
Kini nga topology, pinaagi sa individual cell-level independent control, fundamentally eliminates ang inherent shading effects ug battery balancing issues sa tradisyonal nga series structures sa physical level. Pinaagi sa proper component selection, ang sistema allows ang PV cells mogamit near sa ilang Maximum Power Point (MPP) consistently, thereby eliminating the need for additional MPPT circuits ug complex Battery Management Systems (BMS).

​III. Hierarchical Monitoring Strategy​

Gi-adopt niining solusyon ang hierarchical control strategy aron makamit ang refined monitoring gikan sa local hangtod sa global levels.

​3.1 Module-Level Monitoring Strategy (Autonomous Control)​​
Ang bawat module autonomously switch sa sumala sa iyang kaugalingon nga status (PV output voltage, battery voltage):

​3.2 String-Level Monitoring Strategy (Voltage Coordination Control)​​
String-level monitoring gigamit ang DC/DC converter's input voltage (U_in) isip key parameter, stabilizing voltage pinaagi sa 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, ang 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, ang 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.