Image for illustrative purposes
HARMONIC MITIGATION
When the U.S. government announced a commitment to install 500,000 public EV charging stations by 2030 as part of the 2022 Infrastructure Bill, the news certainly piqued the interest of EV drivers and those considering EV adoption. There’s no question the utility industry and electrical engineers responsible for system health have a keen interest in this development as well.
However, it’s still very early in the plan, and so far, there’s no single entity responsible for implementing it. Building out EV charging infrastructure of this scale will require collaboration from many stakeholders — from power system equipment manufacturers to property owners, local governments, building managers and network providers. Many stakeholders, including electrical engineers responsible for power distribution, may not become part of an EV charging station project until it is well under way.
This wait-and-see approach could put all stakeholders a step behind when it comes to addressing a major infrastructure requirement: EV charging system reliability. For the transformer industry in particular, now is the time to start investigating how EV charging and other nonlinear loads affect power quality, transformer performance, and overall power system health.
Transformer specialists should plan ahead for harmonics.
EV charging, in particular DC fast chargers, rely on inverter-based resources to convert power from AC to DC. These inverters consume current differently from the voltage waveform supplied. This is referred to as a nonlinear load, which creates power quality anomalies — most notably current distortion known as harmonics. With a high percentage of total load being nonlinear, the current distortion starts to affect the voltage source, often significantly.
These distortions not only disrupt charging equipment (a reliability nightmare for drivers), but they also damage connected equipment including transformers.
While the EV charging load may not be excessive, the harmonics produced during charging could lead to an overload situation that heats up the core of the transformer, resulting in premature equipment failure. One study of EV charging installation scenarios noted that a transformer feeding highly distorted current may need to be derated by up to 50%.[i] Given that charging equipment uptime is a prerequisite of publicly funded EV charging infrastructure projects,[ii] an offline station represents financial loss, commercial impact to the charging network operator, and negative user experiences.
[i]Y. Xu, Y. Xu, Z. Chen, F. Peng and M. Beshir, "Harmonic analysis of electric vehicle loadings on distribution system," 2014 IEEE International Conference on Control Science and Systems Engineering, Yantai, China, 2014, pp. 145-150, doi: 10.1109/CCSSE.2014.7224526.
[ii] The White House, Fact Sheet: Biden-Harris Administration Announces New Standards and Major Progress for a Made-in-America National Network of Electric Vehicle Chargers, February 15, 2023
While the EV charging load may not be excessive, the harmonics produced during charging could lead to an overload situation that heats up the core of the transformer, resulting in premature equipment failure.