page_title: Variable-frequency drive
section_title: Regenerative drives
hierarchical_section_title: Variable-frequency drive / Application considerations / Regenerative drives
caption_attribution_description: English: 2010 toyota Prius hybrid electric drive system. Adapted from: Oak Ridge National Laboratory's links - http://ecee.colorado.edu/~ecen5017/notes/OakRidge_2010Prius.pdf - http://k0bg.com/images/pdf/890029.pdf James Glover's http://www.midmichigansae.org/documents/DrGoverPresentationSAEApril20.pdf Dave Wilson's http://www.freescale.com/files/training_pdf/WBNR_ENERGY_REGENERATION.pdf
context_page_description: A variable-frequency drive or adjustable-frequency drive, variable-voltage/variable-frequency drive, variable speed drive, AC drive, micro drive or inverter drive is a type of adjustable-speed drive used in electro-mechanical drive systems to control AC motor speed and torque by varying motor input frequency and voltage.
  VFDs are used in applications ranging from small appliances to large compressors. About 25% of the world's electrical energy is consumed by electric motors in industrial applications. Systems using VFDs can be more efficient than those using throttling control of fluid flow, such as in systems with pumps and damper control for fans. However, the global market penetration for all applications of VFDs is relatively small.
  Over the last four decades, power electronics technology has reduced VFD cost and size and has improved performance through advances in semiconductor switching devices, drive topologies, simulation and control techniques, and control hardware and software.
  VFDs are made in a number of different low- and medium-voltage AC-AC and DC-AC topologies.
context_section_description: Regenerative AC drives have the capacity to recover the braking energy of a load moving faster than the designated motor speed (an overhauling load) and return it to the power system.
  Cycloconverter, Scherbius, matrix, CSI, and LCI drives inherently allow return of energy from the load to the line, while voltage-source inverters require an additional converter to return energy to the supply.
  Regeneration is useful in VFDs only where the value of the recovered energy is large compared to the extra cost of a regenerative system, and if the system requires frequent braking and starting. Regenerative VFDs are widely used where speed control of overhauling loads is required.
  Some examples:
  Conveyor belt drives for manufacturing, which stop every few minutes. While stopped, parts are assembled correctly; once that is done, the belt moves on.
  A crane, where the hoist motor stops and reverses frequently, and braking is required to slow the load during lowering.
  Plug-in and hybrid electric vehicles of all types (see image and Hybrid Synergy Drive).
caption: Simplified Drive Schematic for a Popular EHV[84]
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