safety modes

HSEM Safety Modes and Hardware Write Protection

This document describes the layered safety system that protects the Huawei Solar hardware from unsafe or incomplete planner inputs.

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Safety layers

HSEM has four independent safety mechanisms:

Layer 1: Degraded Mode Classification  (utils/degraded_mode.py)
Layer 2: Read-Only / Dry-Run Gate       (config, switch entity)
Layer 3: Write-Verify Applier           (utils/inverter_verify.py)
Layer 4: Runtime Recommendation Resolver (custom_sensors/recommendation_resolver.py)

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Layer 1: Degraded mode classification

Every update cycle, the state collector classifies the system health into one of three states:

Mode	Writes allowed	Meaning
OK	✅ Yes	All required entities are present and readable
Degraded	✅ Yes (with warnings)	Non-critical data missing (e.g. tomorrow's prices)
Error	❌ Blocked	Critical data missing — hardware writes are blocked

Critical entities (trigger Error mode)

If any of these entity labels appear in the missing-entities list, writes are blocked:

• batteries_state_of_capacity — Battery SoC sensor
• batteries_maximum_charging_power — Max charge power setting
• batteries_maximum_discharging_power — Max discharge power setting
• batteries_rated_capacity — Battery nameplate capacity
• house_consumption_power — House load sensor

Non-critical entities (trigger Degraded mode)

All other missing entities produce Degraded mode. The plan is computed and applied, but warnings are logged and surfaced in data_quality.

Examples:

• Tomorrow's price/PV forecast gaps
• EV charger states
• Export price sensor

Classification logic

def classify_degraded_mode(missing_entities, missing_entities_list):
    if not missing_entities:
        return DegradedMode.OK
    for label in missing_entities_list:
        if any(kw in label.lower() for kw in _CRITICAL_KEYWORDS):
            return DegradedMode.Error
    return DegradedMode.Degraded

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Layer 2: Read-Only / Dry-Run gates

Two independent mechanisms block all hardware writes:

Read-only mode

• Set via the switch.hsem_read_only entity
• When on, the applier bypasses all hardware writes
• Useful for: monitoring the planner without taking control of the inverter
• Configurable in the options flow or via the switch entity

Dry-run mode

• Set programmatically via PlannerInput.is_read_only
• Same effect as read-only — blocks writes
• Used internally during testing and diagnostics

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Layer 3: Write-Verify Applier

The WriteVerifyApplier (utils/inverter_verify.py) wraps every hardware write with a read-back verification loop:

1. Check: is_read_only?     → skip if True
2. Check: degraded mode?    → skip if Error
3. Check: inverter unloading? → skip if True
4. Write the desired value via Huawei Solar service call
5. Wait settle time (default 10 s) for inverter to persist
6. Read back the entity state
7. Compare: value matches?  → OK
   - Yes: return ApplyResult.OK
   - No:  retry up to max_retries
8. If all retries exhausted → return ApplyResult.FAILED

Apply status values

Status	Meaning
ok	Read-back value matched desired value within tolerance
unverified	Write accepted but read-back timed out or returned None
failed	All retries exhausted — inverter did not accept the value
skipped	Current value already matched — no write performed

Verified writes

The applier verifies these hardware writes:

1. Battery working mode — select.batteries_working_mode set to the appropriate TOU mode for the current recommendation
2. Grid export power — set_maximum_feed_grid_power_percent adjusted to zero when export should be blocked, or restored to 100 % when allowed
3. TOU periods — set_tou_periods applied according to the current battery schedule

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Layer 4: Runtime recommendation resolver

Applied to the current slot only at hardware-write time. Overrides the planner output with live sensor readings:

Priority	Condition	Action
1 (highest)	Live import price < 0	→ force_export (overrides everything)
2	Current recommendation = batteries_charge_grid	Kept (never overridden)
3	Any EV actively charging	→ ev_smart_charging
4	Battery energy > remaining schedule need	→ batteries_discharge_mode
—	None of the above	Planner recommendation kept

Protection rules

• batteries_charge_grid is never overridden by the runtime resolver
• force_export (negative price) always beats EV charging
• The resolver reads live sensor data that was unavailable at planning time (actual inverter working mode, real-time EV charge state)

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Safety gate interactions

flowchart TD
    A[State collection]
    B[Degraded mode classification]
    C{Health state}
    D[Error mode]
    E[OK or Degraded]
    F[Writes blocked]
    G{Read-only or dry-run?}
    H[Read-only blocked]
    I[Write and verify allowed]

    A --> B --> C
    C -->|Error| D --> F
    C -->|OK or Degraded| E --> G
    G -->|Yes| H
    G -->|No| I

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