Configuring Vfds For Use With The Lmv3; Types Of Vfds: Vector And Volt/Hz - Siemens LMV3 series Technical Instructions

LMV Series Technical Instructions
Document No. LV3-1000

Types of VFDs: Vector and Volt/Hz

Although there are over a hundred different manufacturers of VFDs, two main types of VFDs are
produced by these manufacturers for use on blower motors. These two types are Vector and Volt/Hz.
Vector VFDs can usually be run in either Vector mode or Volt/Hz mode. Vector VFDs are also typically
slightly more expensive than Volt/Hz VFDs for a given size.
The advantage of Vector VFDs is that they provide more accurate torque control of the motor. This
accurate torque control enables much more accurate speed control of the motor, especially at lower
motor speeds. More accurate speed control of the motor enables more accurate, repeatable control of
the airflow.
As mentioned earlier, the LMV3 employs a safety-related speed feedback on the blower shaft, thus
continuously checking and adjusting (if necessary) the signal to the VFD to achieve the desired blower
speed within a certain band. The LMV3 can lockout and shut down the burner if blower speed
deviations are large and persist for too long. Due to their increased accuracy, Vector VFDs provide
trouble-free operation on almost all LMV3 VFD blower applications. Volt/Hz VFDs can work
satisfactorily in some applications, but are not preferred due to their decreased accuracy.
Vector VFDs are typically run in Open Loop Vector (OLV) mode. In this mode, the VFD uses a
mathematical model of the motor combined with extremely accurate, fast scanning of the current and
other data taken from the rotating motor. In reality, Open Loop Vector mode does have feedback, but
the Vector VFD itself does not require a separate encoder to achieve this.
Since Vector VFDs use a mathematic model of the motor, and the design of motors differs somewhat
between motor OEMs, a static or dynamic auto-tune is sometimes required so that the Vector VFD
"learns" key aspects of the motor it is connected to. A static auto-tune (motor is not spun) does not
require that the load (blower wheel) be de-coupled from the motor. A dynamic auto-tune (motor is
spun) typically requires that the load (blower wheel) be de-coupled from the motor, which is not
possible or practical in many situations. A dynamic auto-tune typically generates the best "learning" of
the motor properties. A static auto-tune is typically all that is necessary if speed control issues are
encountered on a vector VFD.

Configuring VFDs for use with the LMV3

Modern VFDs typically have hundreds of parameters that can be set to tailor the VFD to a specific
application. As mentioned earlier, there are also at least a hundred different manufacturers of VFDs,
each of which have their own unique parameter list. Due to these two factors, SCC offers pre-
programmed VFDs that can be purchased with the VFD parameters set up for use with an LMV3.
If a VFD for use with an LMV3 is purchased and programmed independently, the following points will
serve as a general guideline for programming the VFD for the LMV3 application. Note that these
guidelines are necessarily general due to the variety of VFDs offered in the marketplace.
1. If a Vector VFD is used (recommended), set the "Control Method" to Open Loop Vector mode or
equivalent.
SCC Inc. Page 7 Section 5