POWER ELECTRONIC MODULE INTERFACE STANDARDIZATION EFFORT

 

Why Standards

Power electronics circuits are being packaged into modules at higher power densities with internal integration of control electronics. Presently, power electronic modules are designed without compatibility between different manufacturer products. Consequently the development, installation and maintenance (particularly over the long term) of a power electronics system is difficult and costly. The goal of developing power electronics standards is to establish guidelines for power module manufacturers and the user community so that power modules can be interfaced readily and unnecessary retooling cost can be avoided.

 

Why Interfaces

The technology associated with power electronics has changed very rapidly. The advent of the Insulated Gate Bipolar Junction Transistor (IGBT) has enabled a tremendous control capability over the last ten years that was not dreamed of twenty years ago. This development is predicted to continue. There has been work done in the area of materials of devices to allow operation at higher junction temperatures as well as higher current densities. Wide band-gap materials such as silicon carbide promise junction temperatures in excess of 200, up to 300 C. The materials used to package semiconductor devices have changed as well. Large copper base-plates, which dominate today, may yield to metal matrix composites so that reliability and ability to reject heat may be improved.

With these new devices and packaging materials there are new circuit topologies being considered. Today hard-switched PWM is the most common inverter commercially available to control most machines. Resonant converters and matrix are starting to crack the surface. With a technology changing so rapidly does it make sense to try to standardize? The answer is yes.

The one constant throughout these changes is that power electronics modules have to be integrated into power systems that control electric machines and convert power. The power electronics modules, passive elements and intelligent controllers are integrated in a power system. The inside of these blocks may change but the function does not. The interface to the given device, topology, thermal management system (Heat sink, cold plate, etc) remains constant. This is the level to which the industry may develop a standard. By concentrating on the electrical, mechanical, thermal and control interfaces the module may change significantly yet the user may still have a standard footprint to rely on.

 

Why Recommended Practice vs. a Standard or a Specification

A standard development most often begins with a recommended practice. The distinction between a standard and a recommended practice is that the recommended practice is a guideline while a standard should reflect standard, sometimes required, operating procedure within a technology. A standard should be arrived at with rigor and with broad industry acceptance. As a result the most successful standards are the ones that develop in an industry, are accepted and used for a period of time.

Hardware standards such as Ethernet and other similar technologies evolved in essentially this way. However these are narrow application with tightly coupled technologies. Safety related standards are developed by experts and enforced by law in one way or another. Power systems do not fit either mold and need a different path to standards, a more gradual approach seems appropriate. In order to adopt such a standard it must first be introduced as a recommended practice and tracked to see if it is used. A recommended practice gets reviewed and amended over a period of time and when used consistently it can then be evolved into a standard.

Currently the Institute of electrical and electronic engineers (IEEE) is in the process of developing a recommended practice for power electronic modules as well as passive support circuitry, so that power modules can be interfaced more readily. This IEEE activity is a working group and is known as P1461. The document that will be produced will recommend ways of interconnecting system components.

 

Purpose of the P1461 Activity

The purpose of the activity is to make the power electronics modules interchangeable and interoperable. In doing so the ability to provide the users a wider availability of manufacturers products without a major redesign of the system components such as cold plate, heat exchanger, buss-bars, intelligent interface. Each manufacturer may achieve a proliferation of sales volume. Although a particular manufacturer may no longer "control the socket" they will also have access to other manufacturers sockets.

The intent is to recommend the interfaces for modules not to invent a technology. Any activity needs to be technology neutral. It is not the intent of to help any particular semiconductor business. Whether small or large the activity needs to be business neutral. It is also not the intention of the activity to dilute that specification so that any one can build the module. It must be remembered that the intent is to develop an enabler not a solution. The standard specification may recommend that if a coolant system is used it must retain a specific cleanliness specification such as maximum contaminant particle size as well as how many parts per million is acceptable. It would not however dictate the use of a cooling fluid.

 

The structure of the effort

Need to keep the effort general and in support of the industry and users. So the effort will be broken into pieces and levels. The first (lowest level) is very mechanical and firmly based in current practice. Higher levels are much more abstract, here is the proposed definitions of the levels:

Level 0

Physical Characteristics of the mounting and interconnect

Pin size

Module Height

Bolt pattern

Connectors

Thermal Interface

Level 1

Performance characteristics of the Interface

Current density

Thermal Impedance

Control Signals

Level 2

Test methods

 

What the Output Might Look Like

CONCEPTUAL TABLE OF CONTENTS

Section

1. Scope

2. References

3. Definitions/Glossary

4. Interface Schematic

5. Reference Zones (Voltage and Size? or Power?)

6. Level Zero (Physical)

1. Power Interface

1. Style A (Applicable Zones P, Q Z)

2. Control Interface

1.

3. Thermal Interface

1. Integral liquid cooled heat sink

1.

2. Base-plate Cooled

3. ???

4. Mechanical Interface

1. Bolt Pattern

1.

2. Mass

1.

7. Level One (Performance)

1. Power Interface

1. Style A Zones P & Q

2. Control Interface

1. V1 Electrical Interface Signal Description

1. Electrical Interface Data Signal Definitions

1. Serial Data Protocol

2. Serial Data Definition

2. V2 ----

3. Electrical Interface EMC Specifications

1. Radiated Immunity

2. Radiated Emissions

3. Conducted Immunity (For accessible I/O)

4. ??

3. Thermal Interface

1. Integral Liquid Cooled Heat Sink

1. Pressure drop

2. ??

4. Mechanical Interface

1. Shock, Vibration and Drop Specifications

1. During Operation

2. During Shipping / Handling

2.

8. Level Two (Test Methods)

 

Figures

Tables

APPENDIXES

APPENDIX FIGURES

 

Credits: This paper is a compendium of inputs from many people in the P1461 working group. In particular I would like to note Jeff Fishbein Sunil Chhaya, John Miller and Dennis Darcy.