The power analyser – the essential, virtual toolbox

The demands on power conversion system designers have never been greater than they are today. The market requirements in nearly all applications call for smaller, lighter and higher efficiency devices. Advances in semiconductor technology, passive components and packaging are all contributing to achieving these goals. At the same time, better tools are required to facilitate the design process. Among these tools are the latest generation of advanced technology power analysers. 

Functions and applications

Power analysers combine the precision measurement and recording of a variety of parameters critical in designing and evaluating systems designed to generate, convert and consume electrical energy. Parameters include voltage, current, frequency, harmonics, RFI / EMI, power and efficiency. In addition to performing these measurements, power analysers typically include the capabilities of saving set-up data, producing reports, communicating via digital means with external devices and other power analysers to perform and archive testing of complex systems. Some power analysers have built-in functions to test equipment for compliance with efficiency and emissions standards.

Scope capture and history are valuable tools for short term or long-term characterisation during design and development.  In addition to these product design, development and manufacturing applications, power analysers are also employed in the field to troubleshoot problems and assess performance of systems in operation.

Compliance testing

One special feature, worthy of note, offered on advanced power analysers is the built-in compliance tests for various industry leading environmental performance standards. These compliance tests are integrated into the device’s menu, allowing the instrument to quickly test the device under test for compliance with a selection of environmental / performance standards including EN60034-2-1:2014 (motor drives), EN50564:2011 (standby power), EN61000-3-2 and 3-12 and 4-7 (harmonics emissions), RTCA DO-160E/F/G (avionics), Boeing 787B3-0147, Airbus ABD0100.1.8 (A380) and ABD0100.1.8.1 (A350).

Figure 1: Advanced power analysers accommodate a selection of single phase and multi-phase measurements

Configuration choices

Some applications require the use of a single power analyser, others require simultaneous application of two, three or even four power analyser.

Power analysers are connected between the source and load, as shown in Figure 1. Typically, a single power analyser would be used to measure, depending of the type of power converter, input or output voltage, current, frequency, harmonic distortion, power factor or RFI / EMI. Adding efficiency calculations requires the use of a second analyser or with some advanced devices, e.g the Vitrek PA 920 series, a second channel in the power analyser.

For dual analyser or dual channel applications, where both input and output measurements must be conducted simultaneously, it is frequently necessary to use two power analysers or two power analyser channels, as shown in Figure 2. 

A list of typical applications requiring dual power analysers includes single phase AC to DC power supplies (single or multiple outputs), DC to DC power supplies (single or multiple outputs), DC or fixed frequency AC supplied variable or fixed speed motor drives, power transformers (single or multi-phase), lighting ballasts (most types), standby or back-up power supplies (AC or DC), photovoltaic (PV) power generators (DC in / DC or AC out), electric vehicle (EV) traction motor or generator drive systems.

Figure 2: Two power analysers are needed in applications where both input and output measurements are required

Multiple choices

There are also multiple analyser or multiple channel applications. Complex systems with multiple power conversion stages such as emergency lighting ballasts (most types), standby or back-up power supplies (AC or DC) and solar systems with auxiliary battery back-up require three synchronised power analysers or three virtual power analyser (VPA) channels, as shown in Figure 3. 

Note that in large systems, e.g. distributed power networks, the input power analyser can be placed far away (literally miles) from the output power analyser. In addition, there are very intricate applications, like inductive wireless charging of EV batteries that would require four geographically distributed power analysers.

Figure 3: Double-conversion systems, like this UPS, require three power analysers to characterise performance

The virtual power analyser  

As already noted, many tasks that use power analysers require the simultaneous application of multiple analysers. Advanced power analysers are available with multiple channels allowing for simultaneous measurements to be performed by a single unit. An example is the PA 920 series (Figure 4) which uses partitioning to allow channels to be combined as virtual power analysers.

Examples of the virtual power analyser concept in practice include power supplies. For example, an AC/DC power supply with a three-phase AC input and a DC output could be analysed with a single four-channel power analyser. Three channels would be combined as one VPA to measure and record the three-phase input. The fourth channel would then measure the DC output. All I/O measurements, including efficiency, are contained within one device without any external synchronisation. 

The VPA can also be used on EV drive systems. The analysis of the performance of an EV drive system can be accomplished by assigning two channels each to the interface between the battery and two channels as a second analyser between the power converter and the motor. Bi-directional energy flow, efficiency and a full range of performance features can be handled with a single instrument.

In the case of a PV inverter, the output of the PV cell (DC) can be monitored on one of the four available channels, while the three-phase AC output (output of the power conditioner inverter and converter) can be monitored using the remaining three channels.

Another typical use case is for motor efficiency calculations. Motor manufacturers and users can easily perform efficiency studies to IEC 60034-2-1:2014 which classifies the levels of motor efficiency.

Figure 4: The PA9xx can be equipped with up to four independent channels that can be configured into up three separate power analysers

Considerations

The power analyser combines into a single instrument the functions and features of several benchtop instruments, making it the electronic design engineer’s instrumentation toolbox. In selecting the right power analyser for an application, there are some considerations to bear in mind.

The first is does the instrument offer simple set-up and operation via a touchscreen hi-resolution display?

It is also important to know if the instrument have the required frequency measurement bandwidth. Advanced devices can make both DC measurements and 0.01Hz to over 1MHz supply frequencies.

It is also important to consider if the instrument provides both single phase and multi-phase inputs and if it can accommodate multiple channels.

Other questions are: can the instrument measure bi-directional power flow (per phase and total)? Does the instrument measure and record total power (W, VA, VAR and PF) for all phases in addition to the individual phases? Does it provide harmonic analysis of every signal up to the 500th harmonic?

Other considerations are does the instruments datalogging capabilities provide a scalable time base? What are its report generation capabilities and does the instrument have built-in programming to testing to selected safety and emission standards? 

About the author:

Chad Clark is vice president, sales and marketing at Vitrek. He holds a BE in economics from California State University and has been with Vitrek since 2008. He has worked directly with end users to develop safe methods and procedures enabling countless products to be NRTL safety listed.