A Matrix Converter is an alternative form of power conversion to (Pulse Width Modulation) PWM, but the switching losses in a matrix converter are considerably lower.

C1, C2 and C3 are the terminal pads for the input phases. Within the module, each pad connects to a bidirectional switch (comprising four IGBTs and four diodes): these connect to the common output pad of the module. Each switch is then controlled by four input signals, so for switch 1:

• G1F connects to the gates of two paralleled IGBTs for forward current conduction;
• G1R connects the gates of two paralleled IGBTs for reverse current conduction;
• E1F connects to the emitters of the forward current-conducting IGBTs; and
• E1R connects to the emitters of the reverse current-conducting IGBTs.

S1 and S2 are connected to the output for current direction detection.

Semelab designed the module in accordance with the University of Nottingham’s schematics and Smiths Aerospace’s requirements. The company procured bare die from Infineon but used its own in-house packaging technologies and skills to wire-bond and package the module.

Each module contains 28 separate die and one of the biggest challenges Semelab faced was that of tackling the heat dissipation, and taking heat away from the silicon die without adding stress to the package and impacting overall reliability. Semelab therefore constructed the module using direct bonded copper (DBC) substrates, onto which the die were solder-mounted. The die were then aluminum wire bonded to provide the necessary internal connections.

The power bus bars were embedded into a plastic ring frame and then soldered onto the DBC, which are in turn mounted to the Metal Matrix Composite (MMC) base plate, and all electronics were then encapsulated with military spec silicon gel for compliance allowing the wire bonds to expand and contract. Then on top of the silicon gel a potting compound is added to give the module mechanical strength.

All of these materials have a similar coefficient of thermal expansion (CTE) match to give excellent reliability, when thermal cycling and running the module under extreme conditions.

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