Integration of a Battery Energy Storage System in a Photovoltaic Cascaded H-Bridge Inverter
Author
Sirico, Chiara
Term
4. term
Education
Publication year
2019
Submitted on
2019-05-31
Abstract
Photovoltaic generation is intermittent and subject to partial shading, challenging grid-connected inverters. This thesis investigates integrating a battery energy storage system (BESS) into a photovoltaic cascaded H-bridge (PV-CHB) inverter at the sub-module level. Two modular PV-BESS topologies are proposed: (1) a BESS connected through a dedicated bidirectional dc-dc converter, and (2) a BESS placed directly in parallel with the sub-module dc-link capacitor; in both cases the PV module is interfaced via a boost converter with MPPT. The systems are modeled, operating modes are examined, and a numerical study in PLECS evaluates feasibility, efficiency under different irradiance levels, and European efficiency, alongside CHB control using nearest-level modulation, grid-current regulation, and capacitor-voltage balancing via sorting. Results show that adding the dc-dc stage decreases overall efficiency but enables superior battery-current control and reduced internal battery losses; the direct-parallel topology is more efficient but imposes challenging safety-critical control requirements. Consequently, the dc-dc topology is used to assess operation under partial shading: the grid-side power can be kept constant during sharp irradiance drops on a single panel, while the implemented strategy induces state-of-charge imbalances among sub-modules. Future work should explore SOC-based sorting to support sustained balanced operation.
Fotovoltaisk elproduktion er ujævn og påvirket af delvis skygge, hvilket udfordrer nettilsluttede invertere. Dette speciale undersøger integration af et batterienergilagringssystem (BESS) i en fotovoltaisk kaskadekoblet H-bro (PV-CHB) inverter på submodulniveau. To modulære PV-BESS-topologier foreslås: (1) BESS via en dedikeret, bidirektionel dc-dc-konverter, og (2) BESS direkte parallelt med submodulets dc-link-kondensator; i begge tilfælde er PV-modulet koblet via en boost-konverter med MPPT. Systemerne modelleres, driftsmåderne analyseres, og en numerisk undersøgelse i PLECS vurderer gennemførlighed, virkningsgrad under forskellige irradiansniveauer og europæisk virkningsgrad, sammen med CHB-styring via nearest-level modulation, netstrømsregulering og kondensatorspændingsbalancering med sortering. Resultaterne viser, at den ekstra dc-dc-fase reducerer den samlede virkningsgrad, men giver bedre kontrol af batteristrømmen og lavere interne batteritab; den direkte parallel-topologi er mere effektiv, men kræver en udfordrende styring for sikker drift. Derfor anvendes dc-dc-topologien til at vurdere drift under delvis skygge: neteffekten kan holdes konstant ved skarpe fald i irradians på et enkelt panel, mens den implementerede strategi medfører SOC-ubalancer mellem submodulerne. Fremtidigt arbejde bør undersøge SOC-baseret sortering for vedvarende balanceret drift.
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Keywords