A Modular Test System to Characterize Smart Power Switches
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Author(s):
Dipl.-Ing. Hans-Peter Kreuter -
KAI - Kompetenzzentrum für Automobil- und Industrie-Elektronik GmbH
Wolfgang Gallent - Fachhochschule Technikum Kärnten, gemeinnützige Privatstiftung
Industry:
Mechatronics, Automotive
Products:
CompactRIO, LabVIEW, PXI/CompactPCI, FPGA Module
The Challenge:
Developing an automated test system for the characterization of smart power switches to serve as a basic platform for various measurement tasks focusing on flexibility, modularity, and extensibility of hardware and software.
The Solution:
Designing a system based on PXI and external devices, incorporating PXI matrix switch and relay modules for hardware flexibility, consistently incorporating state machine structures and functional global variables for software flexibility, and encapsulating functional software modules in standardized wrappers with equal interfaces.
"The measurement system is based on a PXI system and external measurement devices; therefore, it can be used as a hybrid measurement system."
Smart power switches are highly integrated components for automotive and industrial applications. For KAI, one major field of activity includes testing and measuring smart power switches and researching their reliability.
We developed an automated test system to characterize smart power devices. Because the system is intended to become a basic platform for various measurement tasks, modularity and extensibility of the hardware and software have been the main focus of our development. We based the measurement system on a PXI system plus external measurement devices so we can use it as a hybrid measurement system. We developed the software in NI LabVIEW.
Motivation for Developing the Test System
We developed the test system for easier and more flexible operation and to reduce costs. No in-depth programming knowledge was required for creating new test sequences because the test sequence generation was based on generic experiment descriptions. Also, it incorporates a graphical user interface for manual test sequence generation and adaption. In addition, the asset cost of a production tester is about € 300,000; the hardware cost of the new test system is about € 50,000, not including the development cost.
Hardware Overview
The test system is mainly based on a PXI system incorporating an embedded controller, the LabVIEW FPGA Module, power supplies, measurement devices such as a voltmeter and multimeters, a function generator, and switching matrix modules. In addition, external devices, including a power supply and an electronic load, are connected via GPIB or USB. Also, we connect a CompactRIO expansion chassis to one of the digital I/O ports of the LabVIEW FPGA Module, which protects digital and analog I/Os.
The LabVIEW FPGA Module permits user-defined triggering, timing, and onboard decision making by providing the start trigger for the measurements of the PXI devices and for the externally connected electronic load.
Device Connectivity
In the interface board for the device under test (DUT), as shown in Figure 1, the input and output terminals of the PXI measurement, signal generation, and power supply devices are connected to the printed circuit board (PCB) by BNC and 2 mm sockets. These I/Os are connected to the switching matrices via a multicore connector, which is the large silver connector on top of the picture. Using the matrices, the I/O channels can be routed to any desired terminal of the DUT, which is connected using a substrate and an adapter PCB (the green PCB). The high current path of the DUT is supplied via power plugs (two green plugs) that connect the power supply and the electronic load via the PXI relay module to the DUT.
Software Architecture
We developed the test system software using LabVIEW. Because the software should become the basis for several different test systems, we carefully considered the modularity and extensibility of the software architecture.
As shown in Figure 2, we divided the instruments in the software architecture into the two device categories of PXI internal devices and externally connected (GPIB, USB) stand-alone devices. Using the device-specific drivers, which can be provided as LabVIEW libraries or APIs, we can implement the encapsulated instruments as functional global variables. Due to the encapsulation of the instrument drivers, the system can interface PXI instruments and external devices and hide the different instrument categories from the upper software layers. In addition to those instrument modules, we implement other functions in the same way including functions for calculations on the measurement data, conditional decisions on the test sequence, loop functions for repeating subsections of a measurement sequence with altering settings, and for outputting acquired data to a file.
In addition to these modules and functions, we implemented the main engine as a so-called queued state machine, meaning its subsequent states are lined up in a queue prior to their execution. A sequence of states defines the measurement task and can be created within the sequence editor user interface or generated out of generic experiment descriptions.
Modularity and Extensibility
To achieve modularity, we frequently use two major software design elements – the “state machine” and “functional global variables” concepts. We encapsulate functional software modules in standardized wrapper modules with common interfaces.
Moreover, instrument modules for controlling measurement devices usually have functions for device initialization, configuration of measurement and trigger settings, reading the measurement data, and shutting down the device resource.
Because of the test system’s modular and extensible architecture, we can adapt and extend it to perform various kinds of measurement tasks. In addition, it is reasonably priced and quick and easy to configure compared to previously used test equipment.
Also, the new test system can interpret generic experiment descriptions used for automated simulation and for production tester measurements.
Lastly, the new test system has a competitive advantage over complex tester equipment and manually configured test and measurement circuitry because it rules out the variation of test results caused by the variation of the test circuitry and user interaction to a certain extent.
This work was jointly funded by the Federal Ministry of Economics and Labour of the Republic of Austria (contract 98.362/0112-C1/10/2005 and the Carinthian Economic Promotion Fund (KWF) (contract 98.362/0112-C1/10/2005).
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