Preprocess Permanent Magnet Synchronous Motor (PMSM) Data and Autogenerate Current Controller Calibration Tables

Use this script to preprocess PMSM data for use in model-based calibration (MBC) and autogenerate current controller calibration tables using the calibratepmsm function. This script produces the table object, MBCdata, for use in MBC. You can import the MBCdata object into MBC from the workspace or use the object with the calibratepmsm function to generate torque tables for a PMSM.

PMSM characterization data can come from a finite element analysis simulation or dynamometer testing.

Import Raw Data

Import the raw PMSM data from an Excel® file.

fileName = "PMSM150kW.xlsx";

Read the units if they are defined in the second row.

opts = detectImportOptions(fileName);
if opts.DataRange=="A3"                 
    opts.VariableUnitsRange = "A2";
end

Read the column-oriented data from the Excel® file to a table.

rawData = readtable(fileName, opts);

Use Standard Names for Required Channels

Save the variable names recognized by the MBC app to the array standardNames. Next, save the variable names from the imported spreadsheet to the array actualNames. Then, replace the imported variable names with the standard variable names. Channel names are read from the top row of the spreadsheet.

standardNames = ["Id", "Iq", "Fluxd", "Fluxq", "Trq"];
actualNames = ["I_d", "I_q", "Psi_d", "Psi_q", "Trq_msr"];
[ok,loc]=ismember(rawData.Properties.VariableNames,actualNames);
rawData.Properties.VariableNames(loc(ok)) = standardNames(ok);

Visualize Raw Data

Visualize the flux linkages data with respect to the d-axis and q-axis currents.

stem3(rawData.Id,rawData.Iq,rawData.Fluxd,"LineStyle","none");
title("Flux d [Wb]");
xlabel("Id [A]");ylabel("Iq [A]");

stem3(rawData.Id,rawData.Iq,rawData.Fluxq,"LineStyle","none");
title("Flux q [Wb]");
xlabel("Id [A]");
ylabel("Iq [A]");

Visualize the torque data with respect to the d-axis and q-axis currents.

stem3(rawData.Id,rawData.Iq,rawData.Trq,"LineStyle","none");
title("Measured Torque [Nm]");
xlabel("Id [A]");
ylabel("Iq [A]");

Define PMSM Specification

Specify the DC voltage Vdc, number of pole pairs pp, resistance Rs , phase peak current IsMax, and maximum modulation voltage VsMax to align with your PMSM specification.

You may need to run tests at different levels of Vdc.

Vdc = 350;
pp = 4;
Rs = 0.0061;
IsMax = 615;
VsMax = Vdc*(2/pi);

Note that VsMax=Vdc*(2/pi) is the maximum fundamental voltage of an inverter drive, calculated by applying a 6-step inverter-controlled voltage to an AC motor and performing a fast fourier transform on the output 6-step waveform. If you apply SVPWM and stay in linear modulation, then VsMax = Vdc/sqrt(3).

Calculate Gridded Data for Id and Iq Axis Currents

Calculate gridded data, [IDgrid,IQgrid], using ndgrid to create a grid for Fluxd and Fluxq, bound by IsMax. The gridded data is used to create the torque contour plot in a later step.

idAxis = linspace(-IsMax,0,51); 
iqAxis = linspace(0,IsMax,51);
[IDgrid,IQgrid] = ndgrid(idAxis,iqAxis);

Define the breakpoints in a cell array.

currentBreakpoints = {idAxis,iqAxis};

Transform Raw Data to Cartesian Coordinate System

Use the fitlookupn function to transform the raw data to the Cartesian coordinates system for these parameters:

• Flux Linkage, Lambdad

• Flux Linkage, Lambdaq

• Torque, measuredTorque

For each transformation, use the breakpoints defined in the previous section, the current column data for id and iq, and the corresponding raw data for the parameter being transformed.

Transform Flux Linkages Data

Transform the flux linkages data and plot the results.

lambdad = fitlookupn(currentBreakpoints,[rawData.Id,rawData.Iq], ...
    rawData.Fluxd,ShowPlot=true);
title("Flux d [Wb]");
xlabel("Id [A]");
ylabel("Iq [A]");

lambdaq = fitlookupn(currentBreakpoints,[rawData.Id,rawData.Iq], ...
    rawData.Fluxq,ShowPlot=true);
xlabel("Id [A]");
ylabel("Iq [A]");
title("Flux q [Wb]");

Transform Torque Data

Calculate the generated torque from the raw flux and current data. Then, transform the calculated and measured torque data and plot the result.

Use a spline approximation of 1 for additional smoothness for the calculated torque and the measured torque.

calculatedTorque = ...
    -1.5*pp*(rawData.Id.*rawData.Fluxq - rawData.Iq.*rawData.Fluxd);
calculatedTorqueGrid = fitlookupn(currentBreakpoints, ...
    [rawData.Id,rawData.Iq], calculatedTorque,1);
measuredTorque = fitlookupn(currentBreakpoints,[rawData.Id,rawData.Iq], ...
    rawData.Trq,1);

Compare Measured and Calculated Torque

Compare the measured and calculated torque. Use a hot colormap (red) for the calculated torque surface.

surf(IDgrid,IQgrid,measuredTorque,"DisplayName","Measured Torque");
cdata = mbcgui.graph.makeCData(calculatedTorqueGrid);
hold on
surf(IDgrid,IQgrid,calculatedTorqueGrid,"CData",cdata, ...
    "DisplayName","Calculated Torque");
title("Torque Comparison [Nm]");
xlabel("Id [A]");
ylabel("Iq [A]");
hold off
legend

Plot Torque Error

Plot the difference in calculated torque and measured torque, resulting in the torque error.

surf(IDgrid,IQgrid,measuredTorque- calculatedTorqueGrid);
title("Torque Error [Nm]");
xlabel("Id [A]");
ylabel("Iq [A]");

Define Operating Points

Specify the number of torque operating points numTorqueLevels and the low torque levels minTorqueLevels. The remaining torque levels are evenly spaced up to the maximum measured torque. Torque is specified in Nm.

numTorqueLevels = 50;
minTorqueLevels = [1 3 6 10 15];

Downsample by a factor of 5.

downsampleFactor = 5;

Specify minimum speed speedMin, maximum speed speedMax, and speed step size speedStep to define speed operating points. Speed does not need to be evenly spaced, but some steps in MBC are easier with evenly spaced speed operating points. Speed is specified in rpm.

Speed is a lookup table input. Match operating points to breakpoints.

speedMin = 1000;
speedMax = 10000;
speedStep = 250;

speed = speedMin:speedStep:speedMax;

Rearrange Data in Torque-Speed Operating Points

Introduce torque as an operating point in addition to speed by rearranging the data to have both torque and speed information.

Calculate Torque Contour Levels

Initialize the torque contours at the levels in minTorqueLevels. Then, evenly space the levels up to the maximum measured torque.

TrqMax = max(abs(measuredTorque),[],"all");
numPoints = numTorqueLevels-length(minTorqueLevels)+1;
torqueLevels = ...
[minTorqueLevels(1:end-1) linspace(minTorqueLevels(end),TrqMax,numPoints)];

Create and Plot Torque Contour

Create and plot torque contour using the contour function.

trqContour is a 2xN array containing sets of contour data for each contour level.

$\left[\begin{array}{cc}{Z}_i& X_i\\ N_i& Y_i\end{array}\right]$

trqContour = contour(IDgrid,IQgrid,measuredTorque,torqueLevels, ...
    "ShowText","on");
title("Torque Contour  [Nm]");
xlabel("Id [A]");
ylabel("Iq [A]");

Rearrange Data by Torque Levels

For each torque level, extract the Trq, Id, and Iq values. Next, downsample data for the torque level. If you have a Signal Processing Toolbox™ license, use the downsample function to calculate dataDownsample. Then, expand each torque level to include all speeds, attaching every speed operating point to each (id, iq) on the torque contour.

start = 1;
accumulatedData = []; 
while start < size(trqContour,2)
    % process each torque levels (the contour levels). 
    % There may be some contour lines missing

    currentTorque = trqContour(1,start);

    % The number of points in the contour for this torque.
    ni = trqContour(2,start);
    stop = start + ni;
    
    % Extract [Trq, Id, Iq] for current torque level.
    torqueData = [repelem(currentTorque,ni) ; 
    trqContour(:,start+1:stop)]'; % [Id, Iq] points for current torque
    
    if false
        dataDownsample = downsample(torqueData,downsampleFactor);
    else
        dataDownsample = torqueData(1:downsampleFactor:end,:);
    end
    
    if ( dataDownsample(end,2)~= torqueData(end,2) ) 
        % Make sure we have the last point in contour
        torqueData = [dataDownsample;torqueData(end,:)];
    else
        torqueData = dataDownsample;
    end
    ni = size(torqueData,1);
    
    % Repeat torque contours for each speed and accumulate data.
    % Make sure speed is a column vector [Trq, Id, Iq, n].
    accumulatedData=[accumulatedData; ...
    repmat(torqueData,[length(speed),1]) repelem(speed(:),ni)];

    % Start of next torque contour.
    start = stop+1;
end

Create Table Object with Preprocessed Data

Store accumulatedData with the variables Trq, Id, Iq, and n to the table, MBCdata.

MBCdata = array2table(accumulatedData,VariableNames=["Trq","Id","Iq","n"]);

Calculate the derived quantities peak current MBCdata.Is, voltage MBCdata.Vs, resultant flux MBCdata.Flux, and maximum flux MBCdata.FluxMax.

Note that MBCData.FluxMax is derived from steady state voltage and torque equations.

MBCdata.Is = sqrt(MBCdata.Id.^2 + MBCdata.Iq.^2);

% electrical speed [rad/s]
we = 2*pi.*MBCdata.n.*pp./60;

Fluxd = interpn(idAxis,iqAxis,lambdad,MBCdata.Id,MBCdata.Iq);
Fluxq = interpn(idAxis,iqAxis,lambdaq,MBCdata.Id,MBCdata.Iq);

Vd = Rs.*MBCdata.Id - we.*Fluxq;
Vq = Rs.*MBCdata.Iq + we.*Fluxd;
MBCdata.Vs = sqrt(Vd.^2 + Vq.^2);

MBCdata.Flux = sqrt(Fluxd.^2 + Fluxq.^2);
MBCdata.FluxMax = ...
sqrt(VsMax^2 - MBCdata.Is.^2*Rs^2 - 4*Rs.*we.*MBCdata.Trq/(3*pp))./we;

Set the units for each of the variables in the MBCdata table object.

                                  % Trq  Id  Iq   n   Is   Vs  Flux FluxMax
MBCdata.Properties.VariableUnits = ["Nm","A","A","rpm","A","V","Wb","Wb"];

Generate Excel Data File for MBC

Check the check box if you want to write data to an Excel file.

Note that unit information will be lost.

if false
    writetable(MBCdata,"PMSM_MBCData.xlsx");
end

Generate Calibration

Automatically generate calibration using data for specified breakpoints using the calibratepmsm function. Run the function from the MATLAB® command line with the option Display=true to show progress and final results in the MBC apps. Note that you cannot use the option Display=true within a Live Script. Do not run this code if you want to manually calibrate the PMSM using the MBC apps.

breakPoints = {speed, [1 4:4:100]};
[optimalTables,results] = calibratepmsm(MBCdata,IsMax,VsMax, ...
    TableType="speedtorquepercent",...
    Breakpoints=breakPoints, ...
    PlotResults=true);

View Lookup Tables

Torque Envelope

Plot the maximum torque envelope using optimalTables.SpeedBreakpoints and optimalTables.TrqEnvelope.

figure
plot(optimalTables.SpeedBreakpoints,optimalTables.TrqEnvelope);
xlabel("Speed [rpm]");
ylabel("TrqEnvelope [Nm]");
title("Maximum Torque Envelope");
grid on

Id Table

Plot the Id Table using optimalTables.TorquePercentBreakpoints, optimalTables.SpeedBreakpoints, and optimalTables.Id_Table.

surf(optimalTables.TorquePercentBreakpoints, ...
    optimalTables.SpeedBreakpoints,optimalTables.Id_Table);
xlabel("Torque Percent [%]");
ylabel("Speed [rpm]");
zlabel("Id Table [A]");
title("Id Table");

Iq Table

Plot the Iq Table using optimalTables.TorquePercentBreakpoints, optimalTables.SpeedBreakpoints, and optimalTables.Iq_Table.

surf(optimalTables.TorquePercentBreakpoints, ...
    optimalTables.SpeedBreakpoints,optimalTables.Iq_Table);
xlabel("Torque Percent [%]");
ylabel("Speed [rpm]");
zlabel("Iq Table [A]");
title("Iq Table");