The Parametric transformer (or paraformer) is a particular type of transformer. It transfers the power from primary to secondary Windings not by mutual inductance coupling but by a variation of a parameter in its magnetic circuit. First described by Wanlass, et al., 1968.

Assuming Faraday's law of induction,

$v(t)=L{\frac {di(t)}{dt))$

it is possible to obtain a voltage at the secondary winding terminals also thanks to a variation of the inductance, so that

$v(t)=I{\frac {dl(t)}{dt))$

This can be accomplished by for example modulating the saturation of the core by means of an applied variable magnetic field. It works even if primary and secondary windings magnetic coupling is zero (when the fluxes are mutually orthogonal) (Burian 1972, p. 278).

S. D. Wanlass, C. L. Wanlass, L. K. Wanlass, "The Paraformer; A new passive power conversion device", IEEE Wescon Tech. Papers, 1968.
Burian, Kurt, "Theory and analysis of a parametrically excited passive power converter", IEEE Transactions on Industry Applications, vol. IA-8, iss. 3, pp. 278–282, May 1972.
Power, Henry Al, "Analysis of a passive power converter as a nonlinear feedback system", IEEE Transactions on Industry Applications, vol. IA-11, iss. 5, pp. 556–559, September 1975.
Bessho, K.; Matsumura, F.; Aoki, Y.; Suzuki, M., "Theory and analysis of a new power converter with center-tap reactor circuit", IEEE Transactions on Magnetics, vol. 11, iss. 5, pp. 1558–1560, September 1975.
Tez, E. Salih; Smith, I. R., The Parametric transformer: a power conversion device demonstrating the principles of parametric excitation", IEEE Transactions on Education, vol. 27, iss. 2, pp. 56–57, May 1984 (includes history of the principle).
Newark Electronics, "Newark-Denver Electronic Supply Co., Wanlass Parax Voltage Regulators and Paraformer" Wanlass "Parax Voltage Regulators and Paraformer," Newark-Denver Electronic Supply Company 1970 catalog pg. 252. Archived at Pro Audio design Forum.

v t e Transformer topics
Topics	Balun Buchholz relay Bushing Center tap Circle diagram Condition monitoring of transformers Electrical insulation paper Growler High-leg delta Induction regulator Leakage inductance Magnet wire Metadyne Open-circuit test Polarity Pressure relief valve Quadrature booster Resolver Resonant inductive coupling Severity factor Short-circuit test Stacking factor Synchro Tap changer Toroidal inductors and transformers Transformer oil Dissolved gas analysis Transformer oil testing Transformer utilization factor Vector group
Types	Autotransformer Buck–boost transformer Distribution transformer Pad-mounted transformer Delta-wye transformer Energy efficient transformer Amorphous metal transformer Flyback transformer Grounding transformer Instrument transformer Current transformer Voltage transformer Isolation transformer Austin transformer Linear variable differential transformer Parametric transformer Planar transformer Rotary transformer Rotary variable differential transformer Scott-T transformer Solid-state transformer Trigger transformer Variable-frequency transformer Zigzag transformer
Coils	Hybrid coil Induction coil Oudin coil Polyphase coil Repeating coil Tesla coil Trembler coil
Manufacturers	ABB General Electric Mitsubishi Electric ProlecGE Schneider Electric Siemens TBEA

Further reading