Power quality issues are expected to become a key concern for utilities as the demand from new and emerging consumer categories such as electric vehicles (EVs) grows. The country has set aggressive targets for rolling out EVs and new commitments are being announced regularly related to policy, technology, finance and partnerships.
One of the key enablers for the rapid uptake of EVs is the development of a widespread charging infrastructure. Distribution utilities must analyse the impact of EV charging on the distribution network (such as distribution transformer loading, increased ohmic losses and accelerated degradation of network components), and identify appropriate locations for EV charging stations to minimise physical network impacts.
Impact of EV charging on power quality
In distribution networks, the typically high resistance to inductance (R/X) ratio of distribution lines, combined with the non-linear load of EVs, can lead to situations where heavy power draw causes a significant voltage dip, possibly exceeding acceptable technical limits. As EVs consume significantly more power than other household loads, they will increase the overall power demand in low voltage grids. In addition, EVs may contribute to coincident load, as drivers are likely to plug in their cars at the same time, during evening or morning system peaks or when low tariffs start to apply.
The non-linear load of EVs and the sudden onset of charging loads may cause voltage unbalance, harmonics and voltage dips, leading to voltage exceeding acceptable limits at various nodes. This degradation in the voltage profile makes the distribution system unstable.
Uncontrolled charging would lead to an increase in peak load demand, transformer overloading and line losses, and power losses will increase as EV penetration grows. Overloading can negatively impact transformer lifespan.
Higher peak loads can cause short-term congestion in distribution grids, adversely impacting the voltage and network capacity. Overloading network equipment can reduce the life expectancy of domestic components and lead to voltage fluctuations outside their designated margins, causing consumers’ devices to malfunction at times of severity.
Solutions for power quality issues
Power quality issues could be preliminarily addressed through several measures. Firstly, the use of automated and controllable tap changers on distribution transformers can alter the power transformer turns ratio in a number of predefined steps, thereby modifying the secondary side voltage.
Another possible solution is to pair EV charging stations with stationary energy storage, which would allow utilities to flatten the electrical load and potentially increase renewable energy usage. Moreover, providing a decentralised/localised energy source for EV charging would reduce congestion in the upstream low tension network and arrest any voltage/frequency dips due to overload/overcharging.
Other solutions include the use of capacitor banks, which are energy storage devices. They store energy as a static charge on parallel plates and improve the power factor. Using static compensators is another solution for addressing voltage dips that exceed certain thresholds. However, this adds to the cost of network augmentation.
Siting and installation considerations can also impact power quality. A location-specific analysis can help identify the needed charging capacity for a particular location. Further, the prioritisation of EV supply equipment (EVSE) locations would depend on the spare capacity of distribution transformers in the feeders connecting the EVSE stations.
Active managed charging – also called vehicle-to-grid integration, intelligent charging, adaptive charging or smart charging – allows a utility or third party to remotely control the EV charging process. Managed charging can reduce grid stress and maintain stability by minimising charging ramp rates and reducing the strain on local distribution transformers.
Lastly, rather than increasing the capacity of the distribution grid, shifting load to the times of day when the grid is underutilised is an effective means of providing additional electricity without investing in grid upgrades. This could be carried out through workplace or business charging, whereby EV users can charge their vehicles during low-demand hours when the grid is typically underutilised, which would not only increase the utilisation factor of the network but also result in reduced technical losses in the distribution system.
In conclusion, rapid advancements in technology due to the proliferation of EV charging infrastructure are reshaping India’s energy landscape. While these innovations promise improved efficiency, sustainability and consumer-centric solutions, they also bring significant challenges, particularly in maintaining power quality. Addressing issues such as grid stability, voltage fluctuations and harmonics requires a holistic approach combining robust policies, targeted investments and technological innovation.