Now available in a General Purpose / NEMA 3R Enclosure!
Many benefits are obtained from devices that use PWM (Pulse Width Modulated) technology, however the output from these devices are square wave forms. Many applications require a more sinusoidal output, thus ruling out these economical and efficient solutions.
The MotorGuard High Performance Output Filter has been designed to be installed at the output terminals of PWM devices. The KMG filter converts the PWM wave form to a near sinusoidal wave form, allowing sensitive applications to take advantage of the efficiencies and savings that PWM output power supplies offer.
Extreme long motor lead lengths. Specific applications can reach 15,000 feet.
Low voltage PWM power supply to medium voltage motor.
Multiple motor applications such as conveyors, blowers, pumps, and fans.
Test floor and test stand applications.
Shore to ship power for non-60 Hz systems.
HVAC systems to include air distribution ducts and fans.
Reduced common mode current
Reduction in bearing currents
Reduction in instrumentation reference to ground
Reduced motor noise, vibration, and heat
Increase in motor life
Elimination of torque ripple
Elimination of voltage wave reflection
Enables systems to meet NEMA MG-1, Part 31 specification
Voltage wave reflection, a function of voltage rise time (dV/dT), occurs due to the impedance mismatch between the output of the PWM power supply and the load. This mismatch causes some portion of the high frequency leading edge to be reflected back in the direction from which it arrived. These reflected waves meet other incoming wave forms, causing higher and higher voltage overshoots. This high voltage can cause early degradation of insulation systems, not only for motors, but also transformers and cables.
The KMG filter is designed to attenuate the carrier components present in the output waveform of typical PWM output power supplies. The general filter topology is an L-C-R low pass circuit. The circuit input is a three phase reactor of sufficient impedance to control the capacitor charging below the inverter peak current fault point. The filter cutoff frequency is set approximately ten times the max allowed fundamental frequency of the inverter to minimize the fundamental KVAR absorbed by the filter while attenuating the carrier components at the rate of 40db per decade. This allows carriers greater than 2KHz to effectively be eliminated from the output of the filter. The purpose of the damping resistor is to control the over voltage excursion at the cutoff frequency to a reasonable level and keep the peak capacitor currents within design limits. An added benefit of the low pass configuration is the capacitive reactance at the load will provide motor power factor improvement thereby improving the overall filter insertion loss to that of the resistor and inductor thermal levels, typically about 2-3% of the inverter full load level.