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Introduction

The dynamic power limiter (DPL) is a software feature allowing automatic inverter power limit adjustments. Depending on the setup, the DPL will take the power meter (i.e. currently consumed power), the available solar power, and the battery charge state into account. Selected inverters are governed such that the currently consumed power (as provided by the power meter) reaches a user-defined value (usually zero). In particular, this allows to implement a zero-export setup.

Systems without battery

The DPL also works in systems that do not have a battery, i.e., where selected inverters are powered by solar panels directly. Configure the DPL accordingly. Battery-related features and settings do not apply for these setups.

Systems without a power meter

Setups without access to a power meter reading are supported. However, this implies that the selected inverters will never produce more than the configured base load.

Refer to the documentation on DPL parameters to learn how to configure the DPL.

Terminology and Basics

Best Effort

The DPL can be slow (>10 seconds) to calculate and send new power limits. With tuning, the limit updates can be as frequent as one or two seconds. There will always be a delay. The DPL cannot be expected to react in "real-time" similar to a commercial inline battery/inverter combination.

Inverters

It is expected that the DPL is in exclusive control over the inverters selected to be governed by the DPL. No other software and no human interaction shall trigger limit updates to be sent to the selected inverters.

Battery Cycles

Reboot State

After a reboot the battery is assumed to be in a charge cycle unless the SoC or voltage is found to be above the respective start threshold.

Charge Cycle

A battery charge cycle is started when the battery SoC or voltage falls below the respective stop threshold. The charge cycle completes when the battery SoC or voltage reaches the respective start threshold. While in a charge cycle, the DPL will not drain the battery.

Discharge Cycle

The battery is or was charged to or beyond the start threshold. The discharge cycle ends when the battery SoC or voltage reaches the respective stop threshold. While in a discharge cycle, the DPL drains the battery to match the household consumption.

Timing

Please be aware that the charge and discharge cycles are not related to a specific time of day, or any time at all. Often, a system is designed such that the battery is empty in the morning, charged during the day, and discharged during the night. However, that is merely a result of the system parameters (solar power installed, battery capacity, inverter output power) and the settings, and not tied to a time of day through software.

Example

Once a discharge cycle starts on day n, the discharge cycle can last to day n+y, if the solar output was high during those days and the battery was able to support the household consumption through all nights.

Exception

The switch allowing to start a discharge cycle at sunset causes switching to a battery discharge cycle when a specific time point, i.e., sunset, is reached. It also causes that the discharge cycle ends at sunrise, if it was started because of this feature, and if it did not end because of the stop threshold during the night anyways.

Voltage Measurements

If the DPL is configured such that voltage thresholds (rather than SoC thresholds) are effective, or when the battery interface fails to provide recent SoC values, the battery's voltage reading is taken from any of the following sources, in the given order:

  1. Battery interface, i.e., the BMS
  2. Victron charge controller battery output terminal
  3. Selected inverter input (configurable)

If available, the battery interface voltage reading is preferred, as it is closest to the actual battery and therefore to be expected to be the most accurate. Without a battery interface and if available, the Victron charge controller output voltage is preferred, as it also is often closer to the battery and more accurate. As a fallback, the inverter's input voltage reading is assumed as the battery voltage.

(Full) Solar-Passthrough

If the currently available solar power is known, the DPL can make additional decisions on how to calculate the inverter limits. See the documentation on (Full) Solar-Passthrough.

Full Solar-Passthrough is implemented separately from the strategy outlined below: All solar-powered inverters are set to 100% output power and the battery-powered inverters are then configured to match the reported solar output power.

Strategy

  1. The DPL calculates the desired total inverter output based on the power meter reading, the inverters' current output (if configured), and the target grid consumption value. If no power meter reading is available, the configured base load is used.
  2. The calculated desired total inverter output is confined by the configured maximum total output.
  3. Solar-powered inverters, if any, are set up with limits such that the desired total inverter output is matched as closely as possible.
  4. The expected output of all solar-powered inverters after their new update is applied is subtracted from the desired total inverter output.
  5. An allowance of DC power is calculated that the battery-powered inverters may consume. The following is a possibly incomplete list of typical scenarios:
    • The battery charge may be below the stop threshold and no solar power is available, so the allowance is zero.
    • Even if the battery is empty, there might be solar power and if Solar-Passthrough is enabled, the allowance is equal to the solar output (adjusted for cable losses).
    • The battery may be charged beyond the start threshold, so the allowance is effectively infinite.
    • Even if the battery is fully charged, the battery discharge limit can reduce the allowance accordingly.
  6. The remaining desired total inverter output is confined by the battery allowance.
  7. Battery-powered inverters, if any, are set up with limits such that the remaining desired total inverter output is matched as closely as possible.

Choosing new limits for the inverters is based on the difference between the current inverters' output of a particular group (solar-powered and battery-powered inverters) and the desired output for that group. The DPL adjusts the output of individual inverters to match the desired output. It adjusts multiple inverters if the change cannot be covered by a single inverter.

The DPL currently prefers inverters to be producing and only shuts down an inverter when necessary to achieve a particular reduction.

Eligible inverters of a group are sorted in descending order of the amount they can add to a particular increase or reduction of output power. This reduces the number of inverters that need to receive an update to implement the change in output power and hence increases the DPL's responsiveness.