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3  BRIDGETEST SYSTEMSUMMARY

HIGH POWER THREE PHASE H BRIDGE TEST SYSTEM

This TDA discusses the electrical and mechanical design of a test instrument for characterizing Three Phase Power Hybrid modules that incorporate power  MOSFET's, IGBTs or Bi-Polar devices. There are three additional pages to this TDA, The Three Phase Bridge Circuit, The Three Phase Test System and the Summary of  Acquired Test Data.  Applications for these modules extend a wide area in the power delivery arena from controlling a variety of permanent magnet brush less motors as well as incorporating several types of Pulse Width Modulation schemes in power supplies. After working in R&D on designing power modules for a few years, I have found that specific test equipment available for this type of component is limited to say the least and most of the test equipment is either limited to a specific application or it is custom built. The test instrument presented in this TDA is versatile enough to be adapted to many applications as well as the capability of testing a variety of different types of single or multi-phase power bridge modules. The test system presented in this TDA has the capability of testing from hundreds of amps down to milliamps with resolutions in the micro-amps. It is also capable of setting delay times for the bridge control, make before break times and is programmable in the 5 ns step increment area. The device is also programmable for any modulation scheme that can be represented mathematically as well as a unique sequence that require manual loading. The test instrument follows the Modular Design Methodology (MDM) which will allow the user to expand its capability when required.

I am also looking at more flexible test systems and software, although I have no problem of purchasing COTS software packages.  My main concerns with COTS software packages are licensing issues as with most COTS packages. Some packages turn off each year and require new licensing fees, personally I avoid these packages as much as possible. Some packages require constant upgrades and are not backwards compatible and sometimes require data conversion for the new releases, I also avoid these.  What I have found is that most of these packages address the more common market needs and not the specialized areas, hence, unless they can be expanded to handle special applications developed by user, I avoid them as well. The cost of developing a custom addition and trying to retrofit a canned package ends up, "in some cases", to be as time consuming as developing the system separately.

Even though some software development is required for a test system of this type, for specialized testing such as this, custom software linked with MathCAD, MatLab or any other math package is generally a better choice. The level of control and flexibility for a specialized system and the propriety nature of development make it a good choice. Most of this system is COTS available, however the sequencer and driver control logic is unique to testing 3 power bridges with MOSFET, IGBT or other semiconductor devices, at least today it is.  A brief outline of the parameters and documentation developed have links below and throughout this TDA,covering the three phase bridge technology and the test system. I have attempted to create this TDA in more of a teaching document than a look what I have done article. A Test System Presentation of this TDA is in PDF format and may be downloaded or read on line. The file is 4.2Meg and if you have a slower connection I recommend just downloading it and reading it off line, just right click and select save as to download the file. All comments are welcome, I can be reached at Sal (JT) through the contacts page in this site. Thanks for taking the time and enjoy the article.    Top

3 H-BRIDGE POWER MODULE FUNCTIONAL BLOCK DIAGRAM

3 BRIDGE TEST SYSTEM BLOCK FUNCTIONAL DIAGRAM

MODULE & TEST SYSTEM OUTLINES

This is where it all begins. We start by outlining the major variables of the test system by understanding the parameters we have to characterize in the unit under test (UUT). Since this is a self contained module that we are either designing or purchasing, some kind of specification or data sheet identifying the devices characteristics should be available. The test system should, at least, be capable of measuring and acquiring data for the module's outlined parameters. Since the module(s) we will be testing incorporate some type of semiconductor device, power MOSFETs, IGBTs, etc., the test system will have to incorporate several types drive circuits to interface with the devices control inputs. Therefore, our device outline will have to be some type of template that will handle a variety of devices, or at least, be able to be modified to handle variances. One of the more difficult tasks for engineers to do is to write a specification outlining parameters or a data sheet for the device under test. Specifications are always updated continually by the marketing and sales departments trying to meet the current industrial market needs. The designer is generally likes to design to a specific set of specifications. Changes cause problems in the design approach and requires rethinking. Therefore, the Test system should be the most flexible of designs and easily expanded.  It would be nice to be able to have the outline created and just fill in the blanks, so our main thoughts are on design methodologies for testing the UUT.

I have put together a typical outline for the power module and the test system that the user may fill in the blanks or add other parameters. After many years of designing products and specifications for many different companies this standard outline evolved, it is one that I would like to see in a specification tech sheet. The Internet, however, has really helped in this by forcing the issue technically,hence, if you do not see it, you just keep looking, there is always someone who will show it. Developing a specific test outline for a device's parameters is similar to developing the test system requirements outline that will be used in measuring the performance of the device itself. Ideally you would like to be able to simulate the actual application conditions for the device, but, in some cases this can be quite challenging or even unrealistic to duplicate. The two tables are the outlines used to develop this test system. However, this TDA will only cover the summary of this project along with some data for proof of concept. The TDA on Permanent Magnet Brushless (PMB) Motors is used to show a typical application that a relates to the development of this test system

Generally, I prefer to publish these reports in PDF format, but, there are still some older systems out there like PDM, which look for jpeg type documents, and to make them in HTML format created too many image conversion files which lead to book keeping issues. Organizing PDF files with web type links are much more manageable. This Test Outline Document is a PDF file and may be downloaded or printed if so desired.

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