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Control Design of a 100‐kW PMSM Drive

TAGS: PSIM Motor Drive Digital Control Motor Control Design Suite EV/ HEV

 

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Table of Contents

 

Overview

The control loop design of a PMSM drive is a non‐trivial task. It involves the design of the inner current loop and outer speed loop. In addition, we must consider motor nonlinearity, and other factors, such as switching and sampling frequencies and motor and drive efficiencies. Also, to achieve optimum performance, we need to develop and implement advanced control algorithms.

The Motor Control Design Suite in PSIM makes this task considerably easier. Pre‐built design templates are provided for linear and nonlinear PMSM and induction machines (IM) with sensored or sensorless control. Based on minimum system specifications, the Motor Control Design Suite automatically designs all the controllers for speed and current loops with properly specified crossover frequencies and stability margins and with advanced control algorithms such as Maximum‐Torque‐Per‐Ampere (MTPA) control, field weakening control, and Maximum‐Torque‐Per‐Volt (MTPV) control. It will generate a complete system that is operational and ready to simulate in minutes.

 

This Application Note

This application note describes how to design an optimized motor drive for a 100‐kW PMSM using the PMSM (IPM) Drive (JMAG‐RT) template. You can find the files for this application note in the folder “Application Notes\Control Design of 100‐kW PMSM Drive” in PSIM.

Please refer to a companion application note Efficiency Map of 100‐kW PMSM Drive (AN002‐01).pdf for efficiency map generation of the motor drive system using this motor.
In this template, the IPM motor is modeled in a JMAG‐RT model. A JMAG‐RT model is derived from JMAG finite element analysis. It delivers a very high level of fidelity and accuracy as compared to the actual motor, with all nonlinear effects (such as saturation, spatial harmonics) included.

Unlike the motor in the linear PMSM drive system, the JMAG‐RT motor in this system is nonlinear, and d‐axis and q‐axis inductances are functions of the motor currents Id and Iq. The JMAG‐RT model provides the nonlinear inductances Ld and Lq  in real-time and feeds them back to various control blocks to achieve optimal control performance.

 

System Specifications

The 100‐kW PMSM is based on the JMAG‐RT motor model PMSM RTML‐034 available from https://www.jmag‐international.com/modellibrary/034/). It has the following parameters:

A 3‐phase inverter with a 500‐V dc bus and 283A current will drive the motor.

 

Step‐by‐Step Design Procedure

Follow the steps below to perform the design.

Step 1: Launch the Design Suite template

In PSIM, go to Design Suites >> Motor Control Design Suite, and select PMSM (IPM) Drive (JMAG‐
RT). Choose the folder to unpack the files. PSIM will load the template as shown below.

The red boxes highlight the Input Parameter Panel of the template and the PMSM block in the JMAG‐RT model. The advanced Speed Control block (also highlighted in red) includes MTPA, field weakening, and MTPV control all in one.

 

Step 2: Load the JMAG‐RT model file

Double click on the PMSM block. The following dialog menu will appear:

Click on the Browse button (highlighted in red above). Select and load the correct JMAG‐RT file for the 100‐kW PMSM, as shown below:

For this JMAG‐RT model, the spatial harmonics model is available. Set the Accuracy Type to Spatial Harmonics to take into account the Spatial-Harmonics-Effect.

 

Step 3: Enter system parameters

Enter parameters of DC Bus, Inverter, Load, Motor, and Motor Controller in the Parameter Panel
based on design requirement, operation conditions, and motor parameters, as shown below:

 

The JMAG‐RT model provides the stator resistance Rs of 0.002 Ohm.

First, you need to determine the proper values of the switching frequency fsw, the sampling frequency fsam of the current loop, and the sampling frequency fsam_w of the speed loop. Then, you need to decide the crossover frequencies fcr_i and fcr_w of the current loop and the speed loop. Typically, fcr_i should be roughly fsam/10 or less, and fcr_w should be roughly fcr_i/10 or less.

For this motor, considering the power level of 100 kW, we choose fsw, fsam, and fsam_w to be 20 kHz, fcr_i to be 1kHz, and fcr_w to be 100 Hz.

Once you entered all input parameters, click on the button Speed‐Torque Curve to see speed‐torque and speed‐power curves of the drive based on the specified parameters, as shown below.

These curves give a very quick glance at the operation boundary of the drive before running any simulation. For example, in this case, the maximum torque is around 210 N*m, and the base speed (the rotor speed where field weakening starts) is around 4400 rpm. You can also change the dc bus voltage and the inverter current, and see how the change affects the torque and power of the drive.

 

Update Parameter File

Click on the button Update Parameter File to update the system parameters for the simulation. The parameter file contains the parameters entered by the user and the ones calculated by the Design Suite, as shown below.

One key feature of the Design Suite is that it automatically calculates the parameters of the current loop and the speed loop controllers, saving you a lot of time and effort in designing the controllers yourself. If you change any of the parameters in the Parameter Panel, you must click on Update Parameter File again to update the parameter file. Otherwise, the parameters will not be updated.

If the back EMF constant Ke is not available, or if you want to double-check the value, we provide a simple open‐circuit test file IPM drive (JMAG‐RT) ‐ back‐emf test.psimsch, as shown below. This circuit runs the motor at 1000 rpm. The peak line‐to‐line voltage will give the value of Ke. For this motor, Ke=80.3 Vpk/krpm.

 

Step 4: Run simulation with the inverter average model

Once you update the parameter file, it is ready to run the simulation. We suggest running the simulation first
using the inverter average model as shown below. Changes to the circuit are highlighted in red.

Since the initial values of fsw, fsam, fsam_w, fcr_i, and fcr_w may not work at the first try, using the average model will exclude the effect of switching and focus on getting the control loops to work first. Also, simulation with the average model is much faster.

You may need to adjust fsam, fsam_w, fcr_i, fcr_w, and the simulation time step to achieve the desired performance.

 

Step 5: Run simulation with the inverter switching model

Once the system works with the inverter average model, change the inverter model back to the switch model to validate the design.

Again, you may need to adjust fsw, fsam, fsam_w, fcr_i, fcr_w, and the simulation time step to achieve the desired performance.

One key simulation waveform to watch is the modulation signal Vma at the input of the PWM block. The waveform Vma should not be severely out of the range of the carrier wave.

Simulation results from this design are shown below.

The Results

The waveforms show the start‐up transient of the 100‐kW IPM drive from 0 to 6000 rpm. In the top left window are the motor currents.

Directly below are the speed reference and the actual speed curves which reach 6000 rpm around 0.8 s.

The trace in the third window on the left is the motor torque. It drops from 200 N*m to 25 N*m (load torque) when the speed reaches the reference value. The torque ripple due to spatial harmonics is clearly visible.

In the bottom window on the left is the modulation signal Vma.

The traces in the top right window are the Id and Iq currents.

The second window on the right shows the Ld and Lq inductances.

Below that are the motor copper loss Ploss_copper, eddy current loss Ploss_eddy, and hysteresis loss Ploss_hys.

The waveform in the bottom window on the right is the operation mode. Before 0.6 s, the drive operates in MTPA control. After 0.6 s, the drive operates in the field weakening control.

As you can clearly see, the motor inductances Ld and Lq vary with the currents Id and Iq. It is important to point out that it is necessary to implement nonlinear control in dq current control loops and PMSM controller where Ld and Lq (both varied with Id and Iq) are fed back to these controllers so that the dynamic nature of Ld and Lq is accounted for in the control loops to achieve better performance.

By replacing the inverter with the inverter module from the Thermal Module, you can obtain device switching losses and junction temperature as well. Together with the power loss of the motor obtained from the JMAG‐RT motor model, you can evaluate the power loss and efficiency of the entire motor drive system.

 

Conclusions

With the Motor Control Design Suite and the JMAG‐RT motor model, you can quickly set up and simulate a PMSM drive system that takes into account all the nonlinearities of a real motor. This greatly helps motor design engineers and control engineers in evaluating the motor performance in a motor drive environment and helps hardware engineers in designing and designing and sizing the inverter.