{
  "node": {
    "id": "term:observability",
    "type": "Term",
    "label": "Observability and controllability",
    "properties": {
      "id": "observability",
      "name": "Observability and controllability",
      "aka": [
        "observability"
      ],
      "section": "topic-state",
      "definition": "Two control-theory properties of a model: whether its internal states can be inferred from its measured outputs, and whether its inputs can steer those states. SOC is poorly observable on LFP’s flat OCV plateau, where voltage barely changes with charge, and the individual SOCs of series cells cannot be steered by pack current alone, which is why balancing exists.",
      "related": [
        "state-observer",
        "state-space-model",
        "ocv-soc-curve",
        "lfp",
        "cell-balancing",
        "voltage-plateau"
      ],
      "url": "https://lemonergy.com/learn/glossary/observability/",
      "mentions": [
        "state-of-charge",
        "open-circuit-voltage"
      ]
    }
  },
  "edges": [
    {
      "id": "edge:6540",
      "source": "term:observability",
      "target": "topic:topic-state",
      "type": "belongsTo",
      "properties": {
        "sourceFile": "terms.json"
      }
    },
    {
      "id": "edge:6541",
      "source": "term:observability",
      "target": "term:state-observer",
      "type": "relatedTo",
      "properties": {
        "sourceFile": "terms.json",
        "meaning": "Related context; not a causal claim"
      }
    },
    {
      "id": "edge:6542",
      "source": "term:observability",
      "target": "term:state-space-model",
      "type": "relatedTo",
      "properties": {
        "sourceFile": "terms.json",
        "meaning": "Related context; not a causal claim"
      }
    },
    {
      "id": "edge:6543",
      "source": "term:observability",
      "target": "term:ocv-soc-curve",
      "type": "relatedTo",
      "properties": {
        "sourceFile": "terms.json",
        "meaning": "Related context; not a causal claim"
      }
    },
    {
      "id": "edge:6544",
      "source": "term:observability",
      "target": "term:lfp",
      "type": "relatedTo",
      "properties": {
        "sourceFile": "terms.json",
        "meaning": "Related context; not a causal claim"
      }
    },
    {
      "id": "edge:6545",
      "source": "term:observability",
      "target": "term:cell-balancing",
      "type": "relatedTo",
      "properties": {
        "sourceFile": "terms.json",
        "meaning": "Related context; not a causal claim"
      }
    },
    {
      "id": "edge:6546",
      "source": "term:observability",
      "target": "term:voltage-plateau",
      "type": "relatedTo",
      "properties": {
        "sourceFile": "terms.json",
        "meaning": "Related context; not a causal claim"
      }
    },
    {
      "id": "edge:mentions/observability/state-of-charge",
      "source": "term:observability",
      "target": "term:state-of-charge",
      "type": "mentions",
      "properties": {
        "sourceFile": "terms.json",
        "method": "build_glossary.mention_index + mentions",
        "field": "definition",
        "meaning": "Text mention; not a causal claim"
      }
    },
    {
      "id": "edge:mentions/observability/open-circuit-voltage",
      "source": "term:observability",
      "target": "term:open-circuit-voltage",
      "type": "mentions",
      "properties": {
        "sourceFile": "terms.json",
        "method": "build_glossary.mention_index + mentions",
        "field": "definition",
        "meaning": "Text mention; not a causal claim"
      }
    }
  ],
  "neighbors": [
    {
      "id": "topic:topic-state",
      "type": "Topic",
      "label": "State estimation",
      "properties": {
        "id": "topic-state",
        "name": "State estimation",
        "lede": "The quantities a battery management system estimates but cannot measure directly.",
        "context": "Distinguish internal states from noisy measurement estimates.",
        "example": "Current-sensor bias accumulates in coulomb counting. Exact model SOC does not establish real estimator accuracy.",
        "lesson_url": "https://lemonergy.com/learn/fundamentals/capacity-and-c-rate/",
        "lesson_label": "Open charge balance"
      }
    },
    {
      "id": "term:state-observer",
      "type": "Term",
      "label": "State observer",
      "properties": {
        "id": "state-observer",
        "name": "State observer",
        "aka": [
          "Luenberger observer",
          "sliding-mode observer",
          "H-infinity filter",
          "adaptive observer"
        ],
        "section": "topic-state",
        "definition": "An algorithm that reconstructs internal states such as SOC by running a model alongside the cell and correcting it with the measured voltage error. A Luenberger observer uses a fixed gain, a sliding-mode observer a switching term robust to model error, an H-infinity filter bounds the worst-case error, and an adaptive observer also updates the model parameters.",
        "related": [
          "kalman-filter",
          "equivalent-circuit-model",
          "state-of-charge",
          "observability",
          "particle-filter",
          "dual-joint-estimation"
        ],
        "url": "https://lemonergy.com/learn/glossary/state-observer/",
        "mentions": []
      }
    },
    {
      "id": "term:state-space-model",
      "type": "Term",
      "label": "State-space model",
      "properties": {
        "id": "state-space-model",
        "name": "State-space model",
        "aka": [
          "state-space representation"
        ],
        "section": "topic-transport",
        "definition": "A model written as first-order equations for a set of internal states — such as state of charge and the voltages across RC pairs — plus an output equation for the measured terminal voltage. Kalman filters and other observers need this form, so equivalent circuit and reduced physics models are cast this way for a BMS.",
        "formula": "ẋ = A·x + B·u; y = C·x + D·u",
        "related": [
          "kalman-filter",
          "equivalent-circuit-model",
          "rc-pair",
          "reduced-order-model",
          "state-of-charge"
        ],
        "example": {
          "title": "Read a one-state thermal model",
          "text": "Let x be temperature rise and u heating power. With ẋ = −0.01x + 0.002u, the time constant is 100 s and a steady 10 W input gives x = 2 K. The output y = x directly reports temperature rise."
        },
        "url": "https://lemonergy.com/learn/glossary/state-space-model/",
        "mentions": [
          "voltage",
          "bms"
        ]
      }
    },
    {
      "id": "term:ocv-soc-curve",
      "type": "Term",
      "label": "OCV–SOC curve",
      "properties": {
        "id": "ocv-soc-curve",
        "name": "OCV–SOC curve",
        "section": "topic-state",
        "definition": "The characteristic relation between a cell’s open-circuit voltage and its state of charge, measured once at low current and stored in the BMS. A steep curve, as for NMC, makes SOC easy to read from voltage; LFP’s flat curve does not.",
        "related": [
          "open-circuit-voltage",
          "state-of-charge",
          "coulomb-counting",
          "lfp",
          "voltage-plateau",
          "ocv-test"
        ],
        "url": "https://lemonergy.com/learn/glossary/ocv-soc-curve/",
        "mentions": [
          "bms"
        ]
      }
    },
    {
      "id": "term:lfp",
      "type": "Term",
      "label": "LFP",
      "properties": {
        "id": "lfp",
        "name": "LFP",
        "aka": [
          "lithium iron phosphate",
          "LiFePO₄"
        ],
        "section": "topic-chemistries",
        "definition": "A positive electrode material, LiFePO₄, giving cells a nominal voltage around 3.2 V, long cycle life and good thermal stability, but less energy per kilogram than nickel-rich oxides. Its flat voltage curve makes state of charge hard to read from voltage alone.",
        "related": [
          "cathode-active-material",
          "nmc",
          "lmfp",
          "ocv-soc-curve",
          "cycle-life"
        ],
        "lesson": "fundamentals/cell-anatomy/#voltage",
        "example": {
          "title": "Chemistry is not the whole datasheet",
          "text": "Two LFP products can differ in format, loading, capacity and current limits. Their cathode family alone does not make them interchangeable."
        },
        "url": "https://lemonergy.com/learn/glossary/lfp/",
        "mentions": [
          "electrode",
          "positive-electrode",
          "nominal-voltage",
          "discharge-curve",
          "state-of-charge"
        ]
      }
    },
    {
      "id": "term:cell-balancing",
      "type": "Term",
      "label": "Cell balancing",
      "properties": {
        "id": "cell-balancing",
        "name": "Cell balancing",
        "section": "topic-state",
        "definition": "Equalising the state of charge of cells in series, since the pack is limited by its emptiest cell on discharge and its fullest on charge. Passive balancing bleeds charge from high cells through resistors; active balancing moves it between cells.",
        "related": [
          "bms",
          "series-parallel",
          "state-of-charge",
          "cell-to-cell-variation"
        ],
        "example": {
          "title": "Pack average versus cell limits",
          "text": "Average pack SOC can look acceptable while one series cell reaches its voltage limit. One aggregate SOC state does not demonstrate cell balancing."
        },
        "url": "https://lemonergy.com/learn/glossary/cell-balancing/",
        "mentions": [
          "active-balancing"
        ]
      }
    },
    {
      "id": "term:voltage-plateau",
      "type": "Term",
      "label": "Voltage plateau",
      "properties": {
        "id": "voltage-plateau",
        "name": "Voltage plateau",
        "section": "topic-charging",
        "definition": "A stretch of the voltage curve where voltage barely changes while charge passes, because the electrode is moving between two phases at a fixed potential. LFP has one long plateau; graphite shows several small ones.",
        "related": [
          "discharge-curve",
          "lfp",
          "phase-transition",
          "ocv-soc-curve"
        ],
        "url": "https://lemonergy.com/learn/glossary/voltage-plateau/",
        "mentions": [
          "electrode",
          "graphite"
        ]
      }
    },
    {
      "id": "term:state-of-charge",
      "type": "Term",
      "label": "State of charge",
      "properties": {
        "id": "state-of-charge",
        "name": "State of charge",
        "abbr": "SOC",
        "section": "topic-state",
        "definition": "How full a cell is, as a fraction of its available capacity. State of charge, like temperature, affects how fast a stored cell ages.",
        "unit": "%",
        "related": [
          "depth-of-discharge",
          "ocv-soc-curve",
          "coulomb-counting",
          "state-of-health",
          "bms"
        ],
        "lesson": "fundamentals/battery-aging/#storage-soc",
        "example": {
          "title": "Interpret a charge inventory",
          "text": "If available capacity is 5 Ah and 3 Ah remains by the chosen estimator, SOC is 60%. A different estimate of available capacity changes this percentage, so compare SOC values only with the capacity convention recorded."
        },
        "url": "https://lemonergy.com/learn/glossary/state-of-charge/",
        "mentions": [
          "usable-capacity"
        ]
      }
    },
    {
      "id": "term:open-circuit-voltage",
      "type": "Term",
      "label": "Open-circuit voltage",
      "properties": {
        "id": "open-circuit-voltage",
        "name": "Open-circuit voltage",
        "abbr": "OCV",
        "section": "topic-state",
        "definition": "The voltage across a cell’s terminals when no current flows and the cell has rested long enough for the voltage to settle. It depends on state of charge and temperature, and a cell whose open-circuit voltage falls unusually fast in storage may have an internal short.",
        "unit": "V",
        "related": [
          "ocv-soc-curve",
          "relaxation",
          "voltage-hysteresis",
          "k-value",
          "internal-short-circuit"
        ],
        "lesson": "fundamentals/cell-production/#finishing",
        "url": "https://lemonergy.com/learn/glossary/open-circuit-voltage/",
        "mentions": [
          "state-of-charge"
        ]
      }
    }
  ]
}