High frequency pulse transformer for an IGBT gate drive

Abstract

A pulse transformer for use in a high frequency motor controller to isolate the electronic control stages from the power stages in a motor controller. The primary and secondary windings are wound on a common ferrite core and spaced apart from one another. The wire size used for the windings is relatively small (gauge 37 or less). Each of the windings has between 10 and 13 turns. The interwinding capacitance must be below 5 picofarads, preferably below 1 picofarad, and most preferably below 0.2 picofarads.

Description

BACKGROUND OF THE INVENTIONU.S. Pat. No. 4,686,437 to Langley et al. entitled Electromechanical Energy Conversion System describes a motor control system whereby a microprocessor or similar electronics can be used to control electric motors. The sensitive electronics are coupled to the motor via a power transistor switching stage wherein the transistors operate in on / off fashion to control the current flow to the motor windings in accord with control signals from the microprocessor. The microprocessor receives feedback from the motor indicating rotor position and other controllable parameters. The microprocessor may also receive command signals usable for servo control. The command signals and the feedback signals are compared to determine the frequency, amplitude and phase for the winding energization, and the rotor position feedback is used to determine the proper commutation of the winding excitation. The microprocessor, either alone or with other components, provides on / off cont...

AI Technical Summary

Benefits of technology

An object of the present invention is to provide improved isolation between the sensitive electronic stages and the associated power stages.

Still another object of the invention is to provide an isolation transformer for a motor controller operating at a high power switching rate in the range above 6 KHz with little high frequency power loss and negligible noise generation.

Yet another object is to provide a pulse transformer for a motor controller with higher system efficiency, i.e. maximum torque, relative to energy applied to the controller.

The pulse transformer in the form of a dynamic coupling inductance according to the invention includes spaced apart primary and secondary windings wound around a common high permeability core. The flux return path for flux through the core is configured to surround the windings. The core is configured so that the core is saturable in normal operation. The windings are spaced as far apart as possible to minimize the inter-winding capacitance. The windings are wound using a small number of turns and small views wires to minimize the surface area of the winding to thereby reduce winding to shell and winding to winding capacitance.

The coupling between the electronic and power stages according to the invention results in a very high rejection of common mode noise and elimination of the related energy absorption. Contrary to conventional design, the primary and secondary windings are located on a ferrite core and separated as far as possible to minimize inter-winding capacitance. A minimum number of winding turns and a small diameter wire are used for the winding to minimize the conductive surface area. Although this structure provides relatively poor magnetic coupling between the windings, it is sufficient since only the leading and trailing edges of the pulses actually pass through the transformer.

Problems solved by technology

In the higher horsepower ranges inefficient use of components and inefficient overall system design directly translate into high controller costs and high usage costs.

However, the problems associated with operating the power stages at higher switching frequencies have proven to be either insolvable or prohibitively costly both in space and money.

High frequency noise can bleed off power from the system and seriously affect the system efficiency.

Noise of the common mode variety (noise that goes up and down together on a parallel conductor pair), can be particularly difficult to detect and even more difficult to eliminate.

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