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A brief side-by-side comparison of the pros and con's of Volts Hertz vs Sensor less Vector VFD control modes and why it's important to use the right motor.
What is the difference between the GS4 Drive’s Volts Hertz and Sensorless Vector motor control modes and which should you use each one? Let’s look at Volts Hertz first. One of the cool things you can do with the GS4 drive is you can modify the volts Hz curve to suit your applications needs. It defaults to the usual straight line Voltage Frequency curve or you can change it to High Starting Torque, Fans and Pumps, Make your own custom curve or use one of the power curves. All of which optimizes the drives output for your application which saves you money. You can use it to control multiple motors at the same time. Since the Volts Hertz doesn’t require any tuning – though it is recommended – it’s super easy to setup and use. Just enter the motor parameters and go. Volts hertz can be used with pretty much any inexpensive 3-phase AC induction motor. The downside with Volts Hertz control is if the load does increase, the motor will slow down because the Drive has no way of knowing what the motor is doing. It just blindly pumps out the voltage and frequency it thinks the motor needs to run and just assumes the motor will do what it is told. And a Volts Hertz drive can typically only control a motor down to around 2-3% of its max frequency. Which for an 1800 rpm motor means a Volts Hertz drive really can’t control the motor below around 30 to 50 RPM. Bottom line: A drive configured for Volts Hertz mode, is ideal for Centrifugal Pumps, HVAC Blowers etc. Pretty much whenever you don’t really care if the motor is running at exactly the right speed, you don’t expect varying loads and you just want to move some stuff. A Sensorless Vector drive isn’t really Sensorless – it just doesn’t have an EXTERNAL sensor. Instead it monitors the current of each phase of the motor and uses that to detect what the motor is doing and react accordingly. Which gets you: Tighter Speed Control under varying loads, Higher Starting Torque – up to 200% of rated torque - and lower speed operation, typically down to about 1 percent of the max rated frequency. You will want to tune the drive, but that only takes a few seconds using the GS4’s built in auto tune feature. Sensorless Vector drives can be used with inexpensive AC induction motors BUT if you plan to run the motor at very low frequencies, then you really want a motor specifically designed for Variable Frequency Drive use. Why? Because the general purpose motors are typically fan cooled. If the motor is running at low speed then the fan won’t cool it enough and will either burn up or at a minimum greatly reduce its lifespan. Motors designed for variable frequency drives – we call those “Inverter Duty motors” – have heavy-duty insulation and thermal properties designed to prevent the overheating issues. For example, this general-purpose motor has an insulation class of F, while this inverter duty motor is class H. Those ae NEMA Insulation Class designations and we see that class H buys you another 45 degrees of operation range. That’s the difference between going outside on a 60-degree day and a 100 degree day. Big difference – right? Also, the rotor in an inverter duty motor is specially designed to maximize the drive’s ability to accurately monitor the induced current. And because Sensorless Vector is monitoring and controlling the current in a single motor’s windings, it can only control one motor at a time. So, any application where you need tight speed control and lower frequencies would be ideal for the Sensorless Vector Control mode. Things like printing, textiles, CNC spindles, etc. Now, you CAN do simple feedback control with both of these control modes using the GS4 Drive’s built-in PLC and/or PID functionality – which we cover in other videos. But, those are for monitoring fluid levels, pressure – things like that – not for monitoring motor speed. That should be enough to get you started. Click here to learn more about the GS4 drive. Click here to learn about AutomationDirect’s free support options and click here to subscribe to AutomationDirect’s YouTube channel so you will be notified when we publish new videos.