At a high-level, the majority of testing a UPS relies on knowing the reaction of the UPS to changes on the input side (such as a grid power outage) and changes on the output side (such as an immediate heavy load). Thus, many of the tests performed on a UPS deal with power quality measurements, such as defined by IEEE 519 or IEC 61000 series standards, which cover both continuous and transient operation. The StepWise test execution platform was utilized to allow the customer to develop arbitrary test sequences using the application specific test steps developed for the program.
Our solution used a cRIO to measure both current and voltage from each leg of the 3-phase power (and neutral) by using appropriate cSeries modules connected to various voltage and current test points within the UPS. The cRIO had enough slots to allow a single cRIO to measure a single UPS.
Assessment of continuous operation mainly reviewed the UPS output power quality. Here, it was important to know the amplitude and phase of each leg of the 3-phase power. Synchronous data acquisition between all voltages and current channels was needed for proper timing alignment of collected data points.
Assessment of transient operation was often a review of power ripple and recovery time. For example, in the event of grid power loss, a UPS would switch over to backup power, with the result being a small transient created on the output a UPS. Again, the voltages and currents needed to be collected synchronously to assure that event timing was aligned.
For increased power capacity, the UPSs could be connected in parallel. When ganged together, the continuous and transient behavior of each UPS needed to be compared to the others, in order to capture the behavior of the entire combined system. Consequently, each cRIO (one per UPS) had to share a clock to enable synchronous data collection across all cRIOs. A timing and synchronization module was placed into each cRIO chassis with one cRIO acting as the master clock source and the others being slaved to that clock.
The overall test system architecture has a master PC communicating with each cRIO. Each cRIO was placed in certain activity states by the master PC, such as “arm for measurement”, “transfer collected data”, and “respond with system health”. This arrangement enables the number of cRIO to shrink or grow depending on the number of UPSs being testing in parallel.