Even if the horsepower and FLA are reasonable, but exceed the rating of the drive, the drive will stop the auto-tune and display an error code regarding a data entry error.īecause a VFD’s auto-tuning routine is to probe the motor and not the load, most auto-tunes that require rotating the motor to make measurements also require the motor and load are disconnected during the auto-tune. If the full-load amps are 100 A, but the entered motor size is 40 HP, the drive will throw a fault to stop the routine. Any values input during the auto-tune are checked against the values allowed for the size of drive being auto-tuned and against each other. The most typical error happens before the auto-tune begins. Manufacturers have a separate list of faults that can occur during an auto-tuning routine. Courtesy: Yaskawa What to do when auto-tuning goes wrongĪs with any VFD and motor operation, there can be pitfalls that can trip up the auto-tuning. This can help the drive better anticipate and compensate for changing loads on the motor and lead to more efficient regulation of motor operation.įigure 3: Some of the measured values are used to populate a single-phase induction motor circuit model. The rest of the model can be calculated using other techniques and measurements and then extrapolated into three phases. All three phases should be the same.įor instance, by applying a dc voltage to the stator and measuring the created current with dc current transformers (DCCTs), the drive calculates the line-to-line resistance, which would be R S in the model. Some of the measured values are used to populate a single-phase induction motor circuit model as seen in Figure 3.
Items that are typically adjusted include: Once the user enters the relevant motor information, the drive prompts the user to start the auto-tuning process during which the drive runs and tests the motor to calculate motor specifications not readily found on the nameplate.Īfter the auto-tune is completed, most VFD makers will allow the user to view a list of modified parameters so it can be simple to do a before and after check of the list to see what was entered and what was measured or calculated. Some specs like slip frequency and leakage inductance are only alluded to on the nameplate and are best calculated by the drive. There isn’t really a need to measure or calculate the full-load amps if the user can just enter it. When the auto-tune function is initiated on the keypad, the drive user needs to enter typical motor nameplate information. The person performing the auto-tune routine is actively involved. It’s a mistake to assume the VFD is does all the work.
Not every manufacturer does auto-tuning the same, but there are common adjustments they all make. Courtesy: Yaskawa What gets changed through auto-tuning Because of this unfamiliarity between the motor and the VFD that auto-tuning becomes the bridge by which good motor information can be passed to the drive.įigure 3: Some of the measured values are used to populate a single-phase induction motor circuit model. It is more the norm that brand A motor will probably be used with brand B VFD. Conversely, the VFD and motor are only sometimes manufactured by a common company. A simple motor code is all the amplifier needs to know everything about the connected motor. The reason for the difference is servo motors and their amplifiers are always bought together from one manufacturer. The VFD auto-tuning asks the load is detached from the motor when the auto-tune is performed. The tuning will help adjust gains for positioning and speed loops. With servo motors and amplifiers (close cousins of the VFD and induction motor), the auto-tuning function will probably have more to do with tuning the servo pair to their loads. As the name auto-tune implies, any operation that calculates and adjusts things automatically at the user’s behest can be called an auto-tune function.
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