European Space Power Conference (ESPC) for 2014

This week’s blog posting is going in a bit of a different direction, as I likewise did last month, to attend and participate in the 2014 European Space Power Conference (ESPC) for 2014. While this was the tenth ESPC, which I understand takes place every couple of years; this was the first time I had opportunity to attend. One thing for certain; this was all about DC power, which is directly aligned with the things I am always involved in. In this particular instance it was all about DC power for satellites and space-bound crafts and probes.

I initially found it just a bit curious that a number of the keynote speeches also focused a fair amount on terrestrial solar power as well, but I supposed I should not be at all surprised. There has been a large amount of innovation and a variety of things that benefit our daily lives that came out of our own space program, fueled by our involvement in the “space race” and still continuing on to this day. (Can you name a few by chance?). This is a natural progression for a vast number of technological advances we enjoy.

At ESPC there were numerous papers presented on solar cells and arrays, batteries and energy storage, nuclear power sources, power conversion and DC/DC converters, super-capacitors, and a variety of other topics related to power. Just a couple of my learnings and observations include:

·         There was a very high level of collaboration of sharing findings and answering questions among peers attending the event

·         While batteries generally have very limited lives, from findings presented, it was interesting to see how well they have performed over extended periods in space, lasting last well in excess of their planned life expectancies. It is a reflection of a combination of several things including careful control and workmanship, understanding life-shortening and failure mechanisms, how to take properly treat them over time, what should be expected, as well as other factors contributing to their longevity. I expect this kind of work will ultimately find its way to being applied to using lithium ion batteries in automotive as well.

·         A lot of innovation likewise continues with solar cell development with higher conversion efficiencies coming from multi-junction devices. Maybe we’ll see this become commonplace for terrestrial applications before long!

·         A number of research papers were presented from participants from universities as well. In all, the quality of work was excellent.

I was there with another colleague, Carlo Canziani. Together we represented some of our DC power solutions there, including our N7905A DC Power Analyzer, N7900 series Advanced Power System (APS), and E4360A series Solar Array Simulator (SAS) mainframe and modules. These are the kinds of advanced power stimulus and measurement test instruments vital for conducting testing on satellite and spacecraft power components and systems.

In all it was a refreshing change of pace to be at an event where power is the primary focus, and if this happens to be an area of interest to you as well, you can find out more about ESPC from their site by clicking on the following link: (ESPC2014). Maybe you will find it worthwhile to attend or even present results of some of your work at the next one as well!

Configuring an Electronic Load for Zero Volt Operation

DC electronic loads are indispensable for testing a variety of DC power sources. There are a number of situations that call for testing DC power sources at low voltage, even right down to zero volts. Often this is also at relatively high current of many tens of amps or greater. Some examples include:

• Low output voltage power supplies and DC/DC converters (mostly for digital circuit power)
• Solar cell I-V testing, down to zero volts
• Fuel cell testing
• Single cell battery testing
• Power supply true output short-circuit testing, down to zero volts

It becomes challenging for the test engineer to find adequate DC electronic loads for low voltage operation, especially at high currents. Many DC electronic loads, including the ones Agilent Technologies provides, use multiple power FETs for their input loading element. While a power FET can actually operate down to zero volts, this is at zero current as well. At high current a few volts is typically needed for stable, dynamic operation at full current.  As one example Figure 1 depicts the input I-V characteristics of an Agilent N3304A DC electronic load.

Figure 1: Agilent N3304A DC electronic load input I-V characteristics

An effective solution for low voltage electronic load operation, right down to zero volts, for the electronic load’s full rated current, is to connect a low voltage boost power supply in series with the electronic load’s input. An example of this set up is depicted in Figure 2.

Figure 2: Zero volt DC electronic load set up

The electronic load now sees the sum of the boost supply’s and DUT’s voltages. Selecting a boost supply having adequate voltage will assure the electronic load will be able to operate at full performance at full current, even when the voltage at the DUT is zero. There are a few things that need to be paid attention to:

• The electronic load needs to dissipate the total power of both the boost supply and DUT
• The DUT needs to be adequately safeguarded against reverse polarity if the electronic load is inadvertently turned on too hard
• The electronic load’s voltage sensing must be able to accommodate the extra voltage difference between the electronic load and DUT, due to the boost supply voltage
• The boost supply ripple and noise (PARD) can contribute to noise measurements made on the DUT

Due to these considerations not all electronic loads may be well suited for zero volt operation with a boost supply so it is necessary to validate if a particular electronic load under consideration can be applied in this manner first.  Further details about zero voltage load operation as well as using Agilent N3300 series DC electronic loads for this purpose are described in product note “Agilent Zero Volt Electronic Load”, publication number 5968-6360E. Click here to access