Low Voltage VFD Motor Drive

Low Harmonic Variable Frequency Drive

Low Voltage Motor Drive

Notes –

  • Projected, based on simulations and BOM for 15 kW prototype, with bi-directional or reverse blocking IGBTs, about 97 % efficiency with standard IGBTs and rectifier grade diodes
  • SJ300-750HFU 100 hp, 480 VAC drive shown at www.driveswarehouse.com, with Trans-Coil KLR 100 hp 5% line reactor, efficiency based on Allen-Bradley ACS800-U1-0100-5 100 hp, 460 VAC drive. VS-PWM is Voltage Sourced – Pulse Width Modulated, with rectifier (6 pulse) input.
  • Same drive, with Trans-Coil Harmonic Guard K-Series 100 hp Input Filter
  • Same drive and input filter, with Trans-Coil KMG MotorGuard Sine Output Filter
  • M-Link current source drive from Princeton Power Systems (http://www.princetonpower.com/products/0610_480V_VSD_competitive_comparison.pdf)
  • IEEE-519 applies to current harmonics on power lines coming in to a plant, but if large fraction of plant load is drives, then each drive must meet IEEE-519, or filtering must be applied at, or near, entrance to plant.
  • High output dv/dt (maximum rate of voltage change) limits allowed line length to motors, and causes higher motor failure rates, in addition to noise
  • Only the UPC isolates the output from the input, allowing the neutral of the output to remain at ground. This reduces insulation stress and completely eliminates bearing currents, allowing for maximum motor life.
  • All rectifier input drives are subject to tripping off-line due to the very common problem of input voltage sags. These drives must do this, even for small, momentary sags, to protect their input sections from large in-rush currents when full voltage returns, since the DC-link voltage of these drives drops very quickly during sags. The UPC drive can maintain full output power with up to 30% momentary sags, and will not ipc vfdtrip with momentary sags to zero volts.
  • Regeneration, the ability to direct power from the motor back to the utility input, can be very useful for controlling high inertia or over-riding loads.
  • High weight and power dissipation suggest that the selling price of the M-Link 100 hp drive is well over $10,000.

Observations –

  • Meeting IEEE-519 is an expensive proposition for standard VS drives, and likely so for non-IPC alternatives.
  • The IPC-UPC drive is projected to cost little more than standard VS drives, with similar size and weight packages, but easily meets IEEE-519, has a nearly sinusoidal output voltage with no common mode offset (no bearing currents and low voltage stress) and low noise operation, with nearly unlimited motor cable lengths allowed, has regeneration as standard, and has no vulnerability to input voltage sags.
  • Using the IPC-UPC drives eliminates the guess work in variable speed drive usage, as there are no uncertainties due to input or output power quality considerations. Total installed cost will typically be lower, as very relatively little engineering is required to determine plant power compatibility.