Power Module

The power module contains a set of functions to calculate quantities of interest for power production and power quality.

Note

The names of the functions below are of the convention path.path.function. Only the function name is used when calling the function in MATLAB. For example, to call on mhkit.wave.io.read_NDBC_file simply use read_NDBC_file.

Characteristics

The characteristics submodule calculates power quantities of interest from voltage and current timseries.

Functions

Description

instantaneous_frequency

Calculates instantaneous frequency of measured voltage

dc_power

Calculates the real power from DC voltage and current.

ac_power_three_phase

Calculates the real power from three phase ac voltage and current.
mhkit.power.characteristics.ac_power_three_phase(voltage, current, power_factor, varargin)

Calculates the real power from three phase ac voltage and current.

Parameters

  • voltage (Time series of all three measured voltages [V]) –

    Pandas data frame

    To make a pandas data frame from user supplied frequency and spectra use py.mhkit_python_utils.pandas_dataframe.spectra_to_pandas(time,voltage)

    OR

    structure of form:

    voltage.voltage : matrix of all three phases

    voltage.time : time vector

  • current (Time series of all three measured current [A]) –

    Pandas data frame

    To make a pandas data frame from user supplied frequency and spectra use py.mhkit_python_utils.pandas_dataframe.spectra_to_pandas(time,current)

    OR

    structure of form:

    current.current : matrix of all three phases

    current.time : time vector

    power_factorfloat

    power factor for the system

    line_to_line: bool (Optional)

    set true if the given voltage measuremtn is line_to_line

Returns

P (Structure)

P.power [W]

P.time

mhkit.power.characteristics.dc_power(voltage, current)

Calculates the real power from DC voltage and current.

Parameters

  • voltage (Time series of  measured voltages [V]) –

    Pandas data frame

    To make a pandas data frame from user supplied frequency and spectra use py.mhkit_python_utils.pandas_dataframe.spectra_to_pandas(time,voltage)

    OR

    structure of form:

    voltage.voltage : matrix or vector

    voltage.time : time vector

  • current (Time series of current [A]) –

    Pandas data frame

    To make a pandas data frame from user supplied frequency and spectra use py.mhkit_python_utils.pandas_dataframe.spectra_to_pandas(time,current)

    OR

    structure of form:

    current.current : matrix or vector

    current.time : time vector

Returns

P (Structure)

P.power [W]

P.gross: gross power from all lines [W]

P.time

mhkit.power.characteristics.instantaneous_frequency(voltage)

Calcultes the instantaneous frequency of a measured voltage

Parameters

um (structure with handles- um.voltage and um.time) – measured voltage source (V) with each timeseries in its own column

Returns

frequency (structure) – frequency of the measured voltage with handles frequency.time and frequency.frequency

Quality

The quality submodule functions assess power quality, including harmonics, interharmonics, and distortion. Calculations are based on IEC TS 62600-30:2018 ED1 and IEC TS 61000-4-7:2008 ED2.

Functions

Description

harmonics

Calculates the harmonics from time series of voltage or current based on IEC 61000-4-7.

harmonic_subgroups

Calculates the harmonic subgroups based on IEC 61000-4-7

total_harmonic_current_distortion

Calculates the total harmonic current distortion (THC) based on IEC/TS 62600-30

interharmonics

Calculates the interharmonics from the harmonics of current
mhkit.power.quality.harmonics(x, freq, grid_freq)

Calculates the harmonics from time series of voltage or current based on IEC 61000-4-7.

Parameters

  • x (structure with x.time and x.current or x.voltage as values) – Time-series of voltage [V] or current [A]

  • freq (double) – Frequency of the time-series data [Hz]

  • grid_freq (int) – Value indicating if the power supply is 50 or 60 Hz. Options = 50 or 60

Returns

harmonics (structure) – harmonic amplitude and frequency of the time-series data

mhkit.power.quality.total_harmonic_current_distortion(harmonic_subgroups, rated_current)

Calculates the total harmonic current distortion (THC) based on IEC/TS 62600-30

Parameters

  • harmonic_subgroups (structure with handles- harmonic_subgroups.amplitude and harmonic_subgroups.harmonic) – Subgrouped current harmonics amplitude indexed by harmonic order

  • rated_current (double) – Rated current of the energy device in Amps

Returns

THCD (double) – Total harmonic current distortion

mhkit.power.quality.harmonic_subgroups(harmonics, grid_freq)

Calculates the harmonic subgroups from the harmonics of current

Parameters

  • harmonics (structure with handles- harmonics.amplitude and harmonics.harmonic) – harmonic amplitude with each timeseries in its own column

  • grid_freq (int) – value indicating if the power supply is 50 or 60 Hz. Valid input are 50 and 60

Returns

harmonic_subgroups (structure with handles harmonic_subgroups.amplitude and) – harmonic_subgroups.harmonic

mhkit.power.quality.interharmonics(harmonics, grid_freq)

Calculates the interharmonics from the harmonics of current based on IEC 61000-4-7.

Parameters

  • harmonics (structure with handles- harmonics.amplitude and harmonics.harmonic) – Harmonic amplitude with each timeseries in its own column

  • grid_freq (int) – Value indicating if the power supply is 50 or 60 Hz. Options = 50 or 60

Returns

interharmonics (structure with handles interharmonics.amplitude and) – interharmonics.harmonic