Typhoon HIL Blog

 From Centralized to Distributed Microgrid

Today, most microgrids are controlled in a centralized fashion with standard master slave architecture. There is a central controller, which is the supervisory controller and is connected via point-to-point connection to every DER in the microgrid.

Researchers from the University of Illinois at Urbana Champaign (UIUC) funded by ARPA-E, have developed a completely distributed controller architecture. Instead of a central controller, multiple micro controllers or nodes communicate with its neighbors towards a consensus. Olaolu Ajala, a PhD student in power and energy systems at UIUC, shows how this distributed controller architecture works using a Hardware-in-the-Loop microgrid testbed.

Sandia National Laboratories is the largest U.S. Department of Energy national lab with over 12,000 employees. It has a major role in supporting inverter development and testing protocols for standards organizations and distributed energy research (DER) vendors. 

Jay Johnson, a principal member of technical Staff at Sandia, leads several renewable energy research projects in the U.S., Europe, and Asia.

He talks about his research paper, “Design and Evaluation of SunSpec-Compliant Smart Grid Controller,” and why Controller Hardware-in-the-Loop (CHIL) is a novel approach. 

Interconnecting distributed energy resources (DER) to the grid, in the United States, requires compliance with a number of standards/grid codes, where three main ones are:

1. National Electrical Code (NEC),
2. Underwriters Laboratories (UL) 1741, and
3. IEEE 1547.

Since the existing versions of UL 1741 and IEEE 1547 (IEEE 1547-2003) were written prior to the development of smart inverters they were being revised in the end of 2016 to cover new grid support, utility-interactive inverters and converters. Revisions of UL1741 and IEEE 1547 came from California. Indeed, in early 2013 regulators at the California Public Utilities Commission (CPUC) and California Energy Commission (CEC) jointly convened the Smart Inverter Working Group (SIWG).

Merriam Webster’s Dictionary defines myth simply as “an idea or story that is believed by many people but that is not true”. Myths are not only the stuff of fairytales and bedtime stories. They also appear in engineering, even in power electronics. Let us now take a closer look at seven HIL402 myths and see how they stack up against reality.

While computer aided design tools have found wide adoption by practicing engineers, control testing has been lagging.

Most of the control system type testing is still done manually, in the lab, using small scale or large full scale power hardware, which can significantly prolong the time it takes to bring new power electronics products to market.

So why do practicing engineers use power hardware to test their control systems in the first place?

One good reason is that until recently there was no satisfactory alternative. Once the real time software is loaded to the DSP and the FPGA starts generating PWM pulses with nanosecond resolution, there is little else what can be done other than hooking it up to their inverters and slowly increasing the voltage, hoping that this time they won't hear a loud BANG.

Luckily, things are improving and powerful, commercially available controller hardware-in-the-loop (C-HIL) test equipment are becoming available. VDC Research Group, a technology market research company, predicted in their report "The Global Market for Hardware-in-the-Loop Testing Solutions" that the adoption of commercial C-HIL solutions for power electronics will depend on the speed at which new C-HIL solutions will be able to replace the in-house developed test rigs industries have been building over the decades.

What is Hardware-in-the-Loop?

Digital control and communication are playing an ever more important role in the field of power electronics and power system. C-HIL (Controller Hardware In the Loop) technology can strongly support this technological evolution  when applied in the learning process at undergraduate and graduate level.

Moreover it makes power engineering more hands on and interactive as well as accessible to undergraduate students because there are no dangers, costs and tight supervision requirements of the power laboratory.

Until recently there were practically no Hardware in the Loop (HIL) systems in the market developed specifically for power electronics and microgrid applications.  

This meant that only large companies in rail and aerospace could afford to add some power electronics HIL functionality on top of their general purpose HIL systems.

Nowadays, with powerful system on chip devices that combine the flexibility of general-purpose processors with the low latency of the FPGA fabric, a multitude of new vendors are competing for their place in this promising market.  

The multitude of competing offers and marketing messages creates confusion with the selection process.  This document will attempt to clarify by pointing out six important criteria that need to be considered when selecting your next HIL system.