FB_PMA_PowerValues_1Ph

The function block FB_PMA_PowerValues_1Ph calculates the power values of the connected consumer. These include the fundamental components and the phase shift angle. Internally, the individual harmonics and their phase angle are determined for the calculations.

Alternatively, the function block FB_PMA_PowerValues_Period_1Ph can be used for the calculation. It uses simpler calculation methods for enhanced dynamics.

The input buffer is provided via the function block FB_PMA_Source_1Ph. The size of the input buffer is half the window length.

By way of example, possible FFT and window lengths are shown in the following table:

FFT length		Window length	Buffer length
512	2⁹	400	200
1024	2¹⁰	800	400
2048	2¹¹	1600	800
4096	2¹²	3200	1600
8192	2¹³	6400	3200
16384	2¹⁴	12800	6400

Memory properties

Since the Welch method is used, in each case the current input buffer together with the last transferred buffer is used for the calculation.

The frequency analysis takes step changes in the time series into account. In order to achieve a correct result, the last two input buffers should therefore be consecutive without step changes.

Syntax

Definition:

FUNCTION BLOCK FB_PMA_PowerValues_1Ph
VAR_INPUT
    nOwnID                : UDINT;
    tTransferTimeout      : LTIME := LTIME#500US;
    stInitPars            : ST_PMA_PowerValues_InitPars;
END_VAR
VAR_OUTPUT
    bError                : BOOL;
    ipResultMessage       : I_TcMessage;
    bNewResult            : BOOL;
    nCntResults           : ULINT;
    fApparentPower        : LREAL;
    fApparentPower_1      : LREAL;
    fApparentPower_1_Min  : LREAL;
    fApparentPower_1_Max  : LREAL;
    fActivePower          : LREAL;
    fActivePower_Min      : LREAL;
    fActivePower_Max      : LREAL;
    fReactivePower_d      : LREAL;
    fReactivePower_1      : LREAL;
    fReactivePower_1_Min  : LREAL;
    fReactivePower_1_Max  : LREAL;
    fTotalReactivePower   : LREAL;
    fPhi                  : LREAL;
    fCosPhi               : LREAL;
    fPowerFactor          : LREAL;
    bValidStatistics      : BOOL;
END_VAR
VAR_OUTPUT PERSISTENT
    stEnergy_Pos          : ST_PMA_Energy;
    stEnergy_Neg          : ST_PMA_Energy;
    stEnergy_Res          : ST_PMA_Energy;
END_VAR

Inputs

The input parameters of this function block represent initialization parameters and must be assigned when declaring the function block instance (alternative: Init method). They may only be assigned once. A change at runtime is not possible.

Name	Type	Description
nOwnID	UDINT	Identifies the function block instance with a unique ID. This must always be greater than zero. A proven approach is to define an enumeration for this purpose.
tTransferTimeout	LTIME	Setting of the synchronous timeout for internal multi-array forwardings. See Parallel Processing in Transfer Tray.
stInitPars	ST_PMA_PowerValues_InitPars	Function-block-specific structure with initialization parameters. The parameters must match the definition of the input and output buffers.

Outputs

Name	Type	Description
bError	BOOL	TRUE if an error occurs.
ipResultMessage	I_TcMessage	The interface offers detailed information about the return value.
bNewResult	BOOL	TRUE once new results have been calculated.
nCntResults	ULINT	Count value is incremented with new output data.
fApparentPower	LREAL	Total apparent power
fApparentPower_1	LREAL	Fundamental apparent power
fApparentPower_1_Min	LREAL	Smallest value of fApparentPower_1 that has occurred. Can be reset via bResetStatistics of the Call method.
fApparentPower_1_Max	LREAL	Largest value of fApparentPower_1 that has occurred. Can be reset via bResetStatistics of the Call method.
fActivePower	LREAL	Active power
fActivePower_Min	LREAL	Smallest value of fActivePower that has occurred. Can be reset via bResetStatistics of the Call method.
fActivePower_Max	LREAL	Largest value of fActivePower that has occurred. Can be reset via bResetStatistics of the Call method.
fReactivePower_d	LREAL	Distortion reactive power
fReactivePower_1	LREAL	Fundamental shift reactive power
fReactivePower_1_Min	LREAL	Smallest value of fReactivePower_1 that has occurred. Can be reset via bResetStatistics of the Call method.
fReactivePower_1_Max	LREAL	Largest value of fReactivePower_1 that has occurred. Can be reset via bResetStatistics of the Call method.
fTotalReactivePower	LREAL	Total reactive power
fPhi	LREAL	Phase shift angle
fCosPhi	LREAL	CosPhi (active power/fundamental apparent power)
fPowerFactor	LREAL	Power factor (active power/total apparent power)
bValidStatistics	BOOL	TRUE if the Min and Max value calculation has been performed. These values are valid.
stEnergy_Pos	ST_PMA_Energy	Energy in positive direction. The output is saved persistently and can be reset via bResetEnergyCalc of the Call method.
stEnergy_Neg	ST_PMA_Energy	Energy in negative direction. The output is saved persistently and can be reset via bResetEnergyCalc of the Call method.
stEnergy_Res	ST_PMA_Energy	Resulting energy. The output is saved persistently and can be reset via bResetEnergyCalc of the Call method.

Methods

Name	Description
Call	The method is called in each cycle to execute the calculations from the input buffer when new data is present.
Init	Alternative to the function block initialization
PassInputs	As an alternative to the Call method, the method can be called in each cycle if no calculation is to take place. The incoming input buffer is then forwarded accordingly.
Reconfigure	The method is called in order to reconfigure the function block during the runtime.
Reset	This method deletes all the data sets already added. In addition, the calculated output values are reset.

Sample

VAR CONSTANT
    cOversamples : UDINT := 10;
    cFFT_Length : UDINT := 4096;
    cWindowLength : UDINT := 3200;
    cSourceInitPars: ST_PMA_Source_InitPars := (
        nBufferLength := cWindowLength/2);
    cPowerValuesInitPars : ST_PMA_PowerValues_InitPars := (
        nFFT_Length := cFFT_Length,
        nWindowLength := cWindowLength,
        fSampleRate := cOversamples * 1000,
        fBaseFreq := 50.0,
        nNumBands := 40,
        fBandwidth := 20.0,
        eWindowType := E_PMA_WindowType.HannWindow,
        fTimeLagCurrentTransformer := 0.0,
        fMinInputCurrent := 0.01);
END_VAR
VAR
    aVoltage AT%I* : ARRAY[1..cOversamples] OF LREAL;
    aCurrent AT%I* : ARRAY[1..cOversamples] OF LREAL;    
    fbSource : FB_PMA_Source_1Ph := (nOwnID := 1, aDestIDs := [2], stInitPars := cSourceInitPars);
    fbPowerValues : FB_PMA_PowerValues_1Ph := (nOwnID := 2, stInitPars := cPowerValuesInitPars);
END_VAR

// Call source
fbSource.Call(ADR(aVoltage), ADR(aCurrent), SIZEOF(aVoltage), 0);

// Call algorithm
fbPowerValues.Call(FALSE, FALSE);

Requirements

Development environment	Target platform	PLC libraries to include
TwinCAT v3.1.4024.0	PC or CX (x86, x64)	Tc3_PowerMonitoring

Further Information