AC drives capable of operating at frequencies of 600 Hz or greater are generally referred to as “high-frequency” drives. These drives are considered by the U.S. and the EU to be dual-use devices, meaning that although they are commonly used in civilian applications, such as industrial equipment, they can also be used in military applications or […]
AC Motors
What are VFD reflected waves and why are they harmful?
Reflected waves, also known as transmission line effects or standing waves, are over-voltages that can damage the motor and cable. The use of IGBTs (insulated gate bipolar transistors) in variable frequency drives has helped to improve VFD performance in several ways. First, their quick switching time (also referred to as rise time, or dV/dt) means […]
FAQ: What is a VFD line reactor?
Many of the components that make up a variable frequency drive (VFD) are semiconductor components, which are sensitive to power or current surges, voltage spikes, line distortion, and general power anomalies. A line reactor is an optional component that can be added to a drive system to protect the VFD and other devices from power […]
What is a rectifier?
AC motors can be operated directly from AC supply voltage, but this is only suitable if the motor is required to run at constant speed. If the speed or load requirements of the motor change, an AC drive — also referred to as a variable frequency drive (VFD) — can vary the voltage and frequency […]
FAQ: What is dynamic braking and when is it used?
When a motor is in an overhauling condition—that is, the load is moving faster than the designated motor speed—the motor acts as a generator and produces electrical energy from mechanical energy. This electrical energy, however, needs somewhere to go, and the most common way of dealing with its release is through dynamic braking. How dynamic […]
FAQ: What are regenerative drives and where are they used?
The main purpose of a motor is to convert electrical energy into mechanical energy. But when the motor’s synchronous speed is less than the rotor speed, the motor acts like a generator and converts mechanical energy into electrical energy. This energy is typically fed back into capacitors in the DC bus, but the bus can […]
FAQ: When are closed-loop and open-loop vector control useful?
AC drives have historically been controlled by a scalar method known as volts per hertz (V/Hz), in which the drive maintains a constant voltage-to-frequency ratio in order to maintain stable torque production. However, the V/Hz control scheme doesn’t allow tight speed regulation and is limited in its ability to produce torque at low speeds. Vector […]
FAQ: What is V/Hz control mode for AC drives?
AC motors are commonly paired with variable frequency drives (VFDs), which control motor speed by regulating the frequency of the supplied voltage. Depending on the application and level of speed regulation required, VFDs can be controlled by either scalar or vector methods. The most common type of VFD control is a scalar method referred to as volts […]
Groschopp announces AC Motor-Control combo with chassis enclosures
Groschopp, Inc. is currently setting apart its AC motor-control combo by implementing strategic compatibility design measures. When matched with Groschopp motors and gearmotors, the DA1225K-0 and DA1215K-0 reduce slip and increase efficiency better than other drives on the market. In addition, these AC controls exhibit the following characteristics: Short circuit protection Input voltage options: 115/208/230 […]
Field oriented control vs. sinusoidal commutation
Brushless AC (BLAC) motors are driven with sinusoidal AC currents, and due to skewed magnets and sinusoidally distributed windings in their stators, they also produce sinusoidal back EMF. Sinusoidal commutation is a common way to control BLAC motors, as it provides a very consistent torque output with little torque ripple. But at high speeds, sinusoidal […]
