IE5 synchronous reluctance (SynRM) motors are becoming increasingly common in industry with their ultra premium efficiency; however, the most important difference of these motors from standard asynchronous motors is that they cannot be run by connecting them directly to the mains. A synchronous reluctance motor must be commissioned with a suitable variable frequency drive (VFD) and with the correct parameters. When the drive parametering is incomplete or incorrect, the motor either does not turn at all, runs unstably, or loses its efficiency advantage. In this guide we cover technically how to select the drive control mode specific to an IE5 SynRM motor, the autotune (automatic identification) process, torque and current limit settings, why drive-motor package compatibility is mandatory, and the commissioning check steps.

IE5 synchronous reluctance motor and variable frequency drive parametering panel

Why Does an IE5 Synchronous Reluctance Motor Not Run Without a Drive?

The rotor of a synchronous reluctance motor contains neither a winding nor a magnet; the rotor turns thanks to the paths the magnetic flux prefers (the reluctance difference). This structure means the motor cannot start on its own. When a standard asynchronous motor is connected to the mains, it starts with its own slip torque; the SynRM motor, however, because it must rotate at synchronous speed, cannot start directly on the mains and must always be controlled by a drive.

For this reason, IE5 SynRM motors are always offered together with a variable frequency drive, often as a matched package supplied by the manufacturer. The drive manages the motor's rotor position and magnetic behaviour to ensure synchronous operation. We detailed the supply and cost advantage of the magnet-free rotor in our magnet-free rotor article, and why the package is inseparable in our drive-motor package and cost article.

Selecting the Correct Control Mode on the Drive

The first and most critical step of commissioning is selecting the motor type correctly on the drive. Modern variable frequency drives offer options in the motor type parameter such as "induction (asynchronous)", "permanent magnet (PM)" and "synchronous reluctance (SynRM)". For an IE5 SynRM motor, the synchronous reluctance control mode must definitely be selected. If the asynchronous mode is selected by mistake, the drive builds the motor's magnetic model incorrectly and the motor either does not turn or runs unstably at low efficiency.

Vector Control and Motor Model

SynRM motors are usually driven with sensorless vector control. The drive uses the motor's electrical model to calculate the rotor position and manages torque precisely. Therefore, the drive must recognize the motor model (inductance values, resistance, etc.) correctly. This is exactly where autotune comes in. We covered the general logic of VFD use on asynchronous motors in our VFD with asynchronous motor article; the SynRM side is a specialized form of this logic.

The Autotune (Automatic Identification) Process

Autotune is the operation in which the drive automatically measures the electrical parameters of the connected motor and loads them into the control model. Autotune is especially important in SynRM motors, because the d and q axis inductances of the reluctance motor form the basis of the motor model. Without a correct autotune, the motor cannot run efficiently and stably.

Static and Rotating Autotune

Autotune can be done in two ways: static (without the motor turning) and rotating (while the motor turns freely). Static autotune is used when the motor remains coupled to the load and is difficult to disconnect, and measures the basic parameters. Rotating autotune gives a more accurate result when the motor can be allowed to turn freely at no load, because the rotor position estimation and magnetic flux calibration become more precise. Determining in advance in your commissioning plan whether the motor can be disconnected from the load clarifies which autotune method will be used.

Verification After Autotune

After autotune is completed, the parameter values should be checked to be within a reasonable range. A wrong connection, a loose terminal or incorrect motor data can cause autotune to give an incorrect result. Therefore, before autotune, make sure the motor connections and nameplate data are entered correctly. We covered the drive and installation compatibility in the transition to an IE5 motor step by step in our drive and installation compatibility commissioning article.

IE5 SynRM motor drive autotune and torque current limit parameter setting

Torque and Current Limit Settings

In drive parametering, the torque limit and current limit are critical settings both for protecting the motor and for meeting the application's needs. The torque limit protects both the motor and the driven machine against overload by limiting the maximum torque the motor can produce. The current limit determines the maximum current the drive and motor will draw.

In SynRM motors the current limit is managed differently from an asynchronous motor because of the motor's magnetic saturation behaviour. A wrong (too low) torque limit causes the motor to be inadequate at a loaded start; a too-high limit causes the mechanical components to be overstressed. Therefore, the limit values must be set according to both the motor's rated values and the application's load profile. Acceleration and deceleration ramps (ramp time) are also important here; in long-inertia loads, setting the ramp times correctly prevents the drive from going into an overcurrent fault. We examined the difference between variable-torque and constant-torque applications in our motor selection in variable-speed applications article.

Why Is Drive-Motor Package (Matched) Compatibility Mandatory?

The most common mistake in IE5 SynRM motors is trying to match the motor with just any drive. The efficiency and performance advantage of the synchronous reluctance motor is achieved only with a drive that supports the motor's magnetic model and is correctly parametered. For this reason, manufacturers usually offer the IE5 SynRM motor together with a compatible drive, as a matched package.

Advantages of the Matched Package

In a matched package, the drive recognizes the motor's parameters out of the factory; this makes commissioning easier, makes autotune reliable, and preserves the efficiency guarantee. In separately purchased motor and drive combinations that do not recognize each other, it becomes difficult to reach the performance promised by the IE5 efficiency class, and the motor may even run unstably. Therefore, when buying an IE5 motor, you should not consider the drive separately but evaluate the package as a whole. We compared the differences between a permanent magnet (PM) motor and SynRM in our PM motor difference article, and the IE5 vs IE4 efficiency difference in our IE5 vs IE4 article.

Cabling, Filtering and EMC Compatibility

The sound operation of an IE5 SynRM motor together with the drive is not limited to parametering; the cabling and electromagnetic compatibility (EMC) between the drive and the motor are also important. Because variable frequency drives perform high-frequency switching, having the cables going to the motor shielded and correctly grounded both reduces interference and protects the motor insulation. Over long cable distances, adding an output filter (dV/dt or sine filter) at the drive output limits the voltage stress on the motor windings.

Grounding is critical for both safety and accurate measurement. Wrong or incomplete grounding can disturb the drive's rotor-position estimation and cause the motor to run unstably. Therefore, checking the grounding and terminal connections before commissioning should not be neglected. You can find practical information on making the motor terminal box and cable connection correctly in our terminal box and cable connection article.

Part-Load Efficiency and Energy Saving

One of the biggest advantages of IE5 SynRM motors is that they can maintain high efficiency even at part load. Many industrial applications do not always run the motor at full load; in variable-load systems such as pumps and fans, the motor often runs at part load. The wide efficiency curve the SynRM motor provides together with the drive increases energy saving in this part-load region. Therefore, when parametering the drive, taking into account the load point at which the motor runs most maximizes the real energy saving.

We detailed the part-load efficiency advantage in our efficiency curve and part load article. We covered the saving provided together with the drive in pump and fan applications in our high-efficiency motor and variable frequency drive article. Using the TCO approach is a correct method to see in how long this saving pays back the investment.

Maintenance and Long Life

Because the synchronous reluctance motor's rotor contains no magnet or winding, problems such as magnet demagnetization or rotor winding failure do not occur; this is an advantage that reduces the motor's maintenance burden. However, as with every drive-operated system, the drive's heat management, fan and filter cleaning, and parameter backup must be done regularly. Keeping a copy of the drive parameters speeds up commissioning in case of a fault or replacement. We covered the maintenance and fault management of the SynRM motor in our maintenance and fault management article.

Commissioning Check Steps

Following a sequential checklist for the sound commissioning of an IE5 SynRM motor prevents errors. First the mechanical connection and alignment, then the electrical connection and terminals, then drive parametering and autotune, and finally the loaded operation test are performed. Skipping this order, for example running under load before autotune, can lead to incorrect results and faults.

At first start-up, the direction of rotation, vibration, heating and current values should be observed. We covered the general motor commissioning steps in our commissioning and first start-up checklist article. To measure the field efficiency of an efficient motor correctly, also see our nameplate vs field efficiency difference article. For the IE5 product family and transition logic, you can review our IE5 ultra premium motor transition guide, and for product categories reach our efficient electric motors page and our home page.

Frequently Asked Questions

Can I run an IE5 synchronous reluctance motor with any variable frequency drive?

Not recommended. The efficiency and performance advantage of a SynRM motor is achieved only with a drive that supports the synchronous reluctance control mode and is correctly parametered. The safest method is to use the matched drive-motor package supplied by the manufacturer; this makes commissioning easier and preserves the efficiency guarantee.

What happens if I run the motor without autotune?

Because the drive cannot build the motor's electrical model correctly, the motor may not turn at all, may run unstably, or may not reach the performance promised by the IE5 efficiency class. Especially in SynRM motors, stable operation cannot be achieved without the d/q axis inductances being recognized correctly; that is why autotune is a mandatory step.

What should I base the torque limit on?

The torque limit is set according to both the motor's rated values and the load profile of the driven machine. A too-low limit causes inadequacy at a loaded start, while a too-high limit overstresses the mechanical components. The safest approach is to evaluate the starting and continuity requirement of your application and stay within the range recommended by the manufacturer.

Get a Quote

For your IE5 synchronous reluctance motor and compatible drive package needs, contact us with your application, power and speed information; we will offer a matched-package recommendation and commissioning support. For a fast quote and technical support, reach us at +90 (532) 345 49 86 or send your request through our contact page.

Commissioning Checklist

  • Did you select the motor type as synchronous reluctance (SynRM) on the drive?
  • Did you enter the motor nameplate data into the drive correctly?
  • Did you complete the mechanical connection and alignment before autotune?
  • Did you determine the appropriate autotune method (static/rotating)?
  • Did you verify the parameter values after autotune?
  • Did you set the torque and current limits according to the application?
  • Did you set the acceleration/deceleration ramps according to the load inertia?
  • Did you make sure the drive and motor are a matched package?
  • Did you observe the direction of rotation, vibration and current at first start-up?