Today’s power systems operate on 50Hz or 60Hz sinusoidal voltage and current signals, but the SCADA systems typically used to monitor and control them have a sampling rate of 2-3 seconds. This lag doesn’t seem significant until you consider the influx of renewable assets with inverter-based systems like solar PV, wind turbines and battery storage being added to the mix. These power electronics operate on the millisecond level and require higher-speed control to maximize their benefits.

Those benefits include things like maximizing solar production while the sun is shining and minimizing grid stability issues when it’s not. Or being able to leverage the exponentially more efficient and rapid response of a battery as compared to a generator’s ramp up rate when extra power needs to be dispatched into the grid. These benefits are being ushered in by the new distributed energy resource (DER) paradigm, where the grid is transitioning from a one-way to multi-directional transactional network. In this new paradigm, 2-3 second latency can make a serious impact on both power quality and financial returns, especially when stretched across a massive network that incorporates thousands of DERs.

Fortunately, the technology for higher-speed control already exists, and one of the linchpins of this tech has been quietly awaiting its spotlight moment since its introduction to transmission grids thirty years ago. We’re talking about phasor measurement units, or PMUs.

Phasor measurement units (PMUs)

First developed in the 1980s, PMUs measure voltage and current where they’re installed on the grid and compute the magnitude and phase of the signals. Each digitized measurement the PMU takes also receives a GPS time stamp accurate to within one microsecond. Such measurements reveal moment-by-moment changes in the status of the network. The relatively inexpensive sensors can be installed at various nodes in a system for accurate snapshots of grid health.

One early drawback of the PMU was the overwhelming amount of data it could produce. When PMUs were first installed on transmission networks, they had to effectively be dumbed down to reduce the amount of data they were serving up. However, today’s computers and data networks can easily handle a larger volume of data—in fact, sophisticated algorithms and artificial intelligence thrive on masses of data, making PMUs the perfect superhero accompaniment to feed the data-hungry requirements of autonomous systems. 

With PMUs already in place across many power transmission systems, all that needs to be done is for them to be turned back on to their full capacity, and for the data to be fed through a sophisticated controller that can analyze and react to the data as quickly as it’s receiving it.

PMUs and grid control software

The data provided by PMUs truly shines when it is paired with advanced grid control software such as is found in a microgrid or renewable power plant controller. Using the IEEE C37.118 communication protocol, the PMU transmits its data (magnitudes, angles, frequency and power flow) over TCP/IP. In addition to the basic information of magnitude and phase angle, a PMU can also be configured to estimate the frequency of an AC voltage signal and even compute real and reactive power flow when both AC voltage and AC current are measured. Using all these data points, the advanced controller can control real and reactive power separately, offering a high degree of precision which as mentioned earlier, matters greatly when dealing with large quantities of DERs or when managing to constraints imposed by a system operator or power purchase agreement.

For a technical dive into how PMUs operate and why they’re the unsung hero of the 21st century power grid, read the whitepaper: Understanding the real value of phasor measurement units.