V/f control is commonly used for systems that do not require precise speed control, such as fans or pumps. Each of these control schemes achieves an application need and/or limits programing involved to get the system up and running. Some applications are simple and only need to run at an approximate speed, while others need precise and dynamic motor control. Why would I adjust the control method?Īdjusting the control method is a function of meeting needs of the motor-drive application. Adding the encoder tells the VFD what the motor is doing and how it is responding to the load. As its name indicate, closed-loop vector control uses a motor encoder to provide precise speed feedback and eliminate any error in VFD control generated by responding to current feedback. However, the simplest way of viewing this control method is to view it as precise motor control without the need for an encoder.Ĭlosed-loop vector control is the most advanced motor control method available. In essence, complicated algorithms are used to monitoring, interpret and respond to current feedback to provide precise motor control. VFDs can implement this control using various different and complicated control schemes. Self-sensing vector control is a control method that provides a more fine-tuned control of the motor’s speed. These V/f patterns can be adjusted to provide high starting torque or reduced to optimize efficiency for variable torque loads that do not require constant voltage to frequency relationships. V/f control fixes the drive’s output to a predefined voltage and frequency curve for the motor to follow as the VFD’s speed command is adjusted.
It is the most basic of the three topologies.
Volts-per-Hertz (V/f) control is the most commonly used motor control method. These control capabilities can be classified into three groups: volts-per-hertz control, self-sensing vector control, and closed-loop vector control. The control method dictates the capabilities enacted by the drive to regulate motor speed. The first setting commonly set by VFD installers is the control method. What is a control method as it applies to VFDs? Control method influence on VFD programmingġ. The below details a list of the top five parameter settings programmed by VFD installers to explain what the settings are and why they’re needed.įigure 1: VFDs have preconfigured overloads to account for many different motor types including 40:1 speed range variable torque loads, 100:1 speed range constant torque loads, and even non-conventional motors such as permanent magnet motors. Typically, no more than a dozen settings are adjusted for an application. In most cases, the VFD’s default settings will be sufficient for an application and not required any adjustment. However, most applications require only the most basic settings to operate the motor. This is because VFDs are designed and engineered to make the complicated simple. Due to these innovations, it is understandable one may be overwhelmed by the prospect of programming a VFDs for their application. Most VFD applications improve system efficiency and provide a return on the VFD investment in energy savings in typically less than a year.Īs with all electronics, VFDs have advanced in capability and function, providing more system control to help eliminate external devices and programmable logic controllers (PLCs). Through VFDs, electric motors can be used to run a wide array of applications to achieve control not possible with across-the-line operation or mechanical means. With VFD-controlled motors, users can optimize system efficiency by matching motor speed to maintain exact system demand. Variable frequency drives (VFD) are electronic devices using fast acting switches or insulated gate bipolar transistor (IGBT) to convert three phase input power to a variable frequency and voltage output for motor speed control. VFD settings contain programming, and five parameter changes account for most applications.