EV Charging and Power Quality in LV Residential Networks — From Individual Charger to Fleet Penetration
| Charger type modelled | Level 2 on-board charger — 7.2 kW, single-phase, household installation |
| Metodologia | Probabilistic model from measured harmonic spectra — Gaussian Mixture Models — validated against real charger measurements |
| Simulation tool | OpenDSS — time-series harmonic power flows at 10-minute resolution |
| Uncertainty modelling | Monte Carlo simulation — variable start charge time, connection state-of-charge, EV location on feeder |
| Dominant harmonic | 3rd harmonic — most intense throughout the charge cycle regardless of penetration level |
| Key finding | Voltage unbalance and network chargeability both increase with EV penetration level — the third harmonic is the primary driver |
| Supraharmonic issue | |
| Critical threshold | Uncontrolled simultaneous residential charging at high penetration levels can push VUF beyond the 2% IN 50160 limit at feeder end buses |
01 Context — The Scale of the Problem
The electrification of road transport is now a policy commitment in most OECD countries, with targets ranging from 30% para 100% EV market share by 2030–2040 in Europe, North America, and Asia-Pacific. The PQ implications of this transition — in terms of harmonics, desequilíbrio de tensão, and supraharmonic emissions on residential LV distribution networks — have been studied extensively in isolation, but the combined picture at the feeder level, accounting for the stochastic nature of charging behaviour, has been harder to quantify.
O 2021 study by Torres et al. in Applied Energy addresses this gap directly. Starting from measured harmonic spectra of a real Level 2 on-board charger, they built a probabilistic model capturing the charger’s non-linear behaviour across the full charge cycle — from initial connection at a high state of charge deficit through to completion — and then deployed this model in Monte Carlo simulations on an OpenDSS residential LV feeder to assess PQ impacts across multiple EV penetration scenarios.
Level 1 charging (1.4–1.9 kW, standard household outlet) produces modest harmonic currents that are easily absorbed by the distribution network. Level 2 charging at 7.2 kW — roughly 4–5 times the power — produces proportionally larger harmonic currents that can saturate the neutral conductor, cause significant third harmonic voltage distortion on the feeder, and contribute to voltage unbalance when distributed unevenly across the three phases. As Level 2 home charging becomes the default for EV owners who park overnight, the transition from Level 1 to Level 2 as the primary residential charging mode represents a step change in the PQ impact on LV distribution networks.
02 The Level 2 Charger as a Non-Linear Load
A Level 2 EV charger is a power electronic converter — specifically a single-phase AC/DC rectifier with power factor correction (PFC) circuitry — that draws current from the grid in a controlled, non-sinusoidal pattern. The harmonic current profile of an EV charger is not constant: it changes throughout the charge cycle as the battery voltage rises and the charger’s control algorithm adjusts the current draw to manage the state of charge transition.
Probabilistic harmonic spectra
Torres et al. characterised the harmonic spectra of a real Level 2 charger across its full charge cycle using laboratory measurements. The key finding was that the harmonic spectra exhibit irregular, probabilistic behaviour — they are not deterministic values that can be represented by a single table of harmonic orders and magnitudes. The charge state of the battery, the grid voltage waveform shape at the moment of connection, and the charger’s internal control state all influence the harmonic spectrum. This is why simplified, deterministic harmonic models of EV chargers — still widely used in planning tools — systematically underestimate the actual PQ impact at the feeder level.
The study represented this probabilistic behaviour using Gaussian Mixture Models (GMM) fitted to the measured spectra — capturing both the mean harmonic content and its variability across connection states. The GMM model was then embedded in the Monte Carlo simulation framework to propagate harmonic uncertainty through to the feeder-level PQ assessment.
A subtlety identified in the broader EV charger literature is that the harmonic emission of an EV charger is not independent of the grid voltage it is connected to. When the LV feeder already contains third harmonic voltage distortion — the “flattened sinusoid” that is typical of residential grids with multiple switch-mode power supplies — this distorted voltage changes the charger’s operating point and can modify some harmonic components by 30–300% compared to what would be measured on a clean sinusoidal supply. This bidirectional coupling means that as EV penetration increases and third harmonic distortion worsens, the charger emissions themselves change — a positive feedback loop that is not captured in standard harmonic superposition models.
03 Third Harmonic Dominance — The Neutral Conductor Problem
Across all penetration levels and all charge cycle states examined in the Torres et al. study, the third harmonic (150 Hz at 50 Sistemas Hz) was consistently the most intense harmonic component in the EV charger current. This is not specific to EV chargers — it is a characteristic of all single-phase switch-mode power supplies, including laptop chargers, LED drivers, and the switched-mode power supplies used in all modern consumer electronics. EV chargers simply add a much larger magnitude of third harmonic current to a network already dominated by triplen harmonics from these smaller loads.
Why triplen harmonics are uniquely dangerous
In a balanced three-phase four-wire system, positive and negative sequence harmonic currents (5ª, 7ª, 11ª, 13ª…) cancel in the neutral conductor — the neutral carries near-zero current. Triplen harmonics (3rd, 9ª, 15ª…) are zero-sequence — they are in phase on all three phase conductors and therefore add arithmetically in the neutral. A perfectly balanced three-phase system with three single-phase EV chargers — one per phase, identical chargers, identical charging state — produces zero positive-sequence neutral current but a neutral current at the 3rd harmonic equal to three times the 3rd harmonic phase current.
The practical consequence is that distribution transformers and neutral conductors in residential LV networks were sized for the fundamental current demand of the connected loads, with a thermal margin for normal unbalance. The introduction of high-density single-phase EV charging creates a systematic neutral overload from triplen harmonics that is entirely outside the design assumptions of existing LV infrastructure.
04 Penetration Levels — The Feeder-End Effect
The Monte Carlo simulation results from Torres et al. demonstrate a consistent spatial pattern across all penetration scenarios: EV charging has negligible effect on voltage quality at the feeder beginning (near the distribution transformer) but can push voltage unbalance beyond the 2% IN 50160 limit at feeder end buses even at moderate penetration levels. This is the impedance argument at scale — the further from the transformer, the higher the feeder impedance, and the more a given harmonic current translates into voltage distortion.
| EV penetration level | Effect at feeder start | Effect at feeder end | 3rd harmonic voltage | VUF risk |
|---|---|---|---|---|
| Low (<10%) | Negligible | Minor increase in VUF | Within limits | Low |
| Medium (10–30%) | Negligible | Detectable VUF increase | Approaching limits | Moderado |
| High (>30%) — uncontrolled | Minor distortion | VUF may exceed 2% | Likely exceeds limits | High |
| High (>30%) — smart charging | Negligible | VUF controlled | Within limits | Low |
The high-penetration, uncontrolled charging scenario — where EV owners plug in immediately upon arriving home and charge at maximum rate — represents the worst-case PQ condition and is also, in the absence of time-of-use pricing or smart charging mandates, the natural behaviour of EV users. Em 30%+ penetration in a residential feeder, simultaneous evening charging creates a peak demand event that is larger than the existing residential peak load, occurs at precisely the same time as the existing peak, and introduces third harmonic content that the feeder impedance translates into voltage distortion at the feeder end. This is not a theoretical risk for future grid planning — it is already happening in high-EV-density residential areas in Norway, the Netherlands, and California.
05 Supraharmonics — The Hidden EV Charger Emission
Beyond the classical harmonic range (até 2 kHz), EV chargers produce supraharmonic emissions in the 2–150 kHz range from their high-frequency PWM switching stages. These emissions are distinct from the classical harmonics addressed by IEC 61000-3-2 and are not currently subject to specific emission limits in the distribution network context.
The interaction between EV charger supraharmonic emissions and the grid network creates two specific problems:
- PLC communication interference — Smart metering, demand response, and EV charging management systems often use power line carrier frequencies in the 9–95 kHz range (CENELEC bands). EV charger switching frequencies can fall directly in these bands, disrupting the communication signals that are intended to manage the EV charging itself — a circular interference problem
- Intermodulation with other devices — When multiple EV chargers with slightly different switching frequencies are connected to the same feeder, intermodulation products appear at sum and difference frequencies — as demonstrated in the CS06 supraharmonics case study. These additional frequency components can interfere with equipment not designed to tolerate this frequency range
- Grid voltage feedback on harmonic emission — The existing third harmonic voltage distortion on residential feeders (from switch-mode power supplies) modifies the EV charger’s operating point, changing its harmonic emissions by up to 30–300% compared to laboratory measurements on clean supplies. This means field measurements at high-density EV installations will differ significantly from type-test measurements on individual chargers
The most effective mitigation for EV-related PQ problems at the feeder level is smart charging — coordinating charge start times, rates, and phase allocation across multiple EVs to avoid coincident peak demand and uneven phase loading. Optimised smart charging can eliminate VUF exceedances at the feeder end that would otherwise occur under uncontrolled charging at the same penetration level, without requiring any hardware mitigation at individual charger or feeder level. Phase-balancing allocation — assigning new single-phase charger connections to whichever phase has the most spare capacity — is the simplest form of smart charging with the highest benefit-to-cost ratio.
06 Power Quality Perspective
The EV charging PQ problem has a specific character that distinguishes it from historical PQ problems: it is a planning problem as much as an engineering problem. Arc furnaces and VFDs are installed by industrial customers who engage with the utility during the connection process — there is a defined point at which PQ assessment happens and mitigation is negotiated. Residential EV chargers are installed by homeowners who connect to whatever outlet is available, at no notice to the distribution network operator, at rates that can double overnight if an incentive programme launches.
The third harmonic dominance finding is immediately useful for distribution engineers assessing existing infrastructure. Neutral conductors in older residential LV networks — particularly those built in the 1960s and 1970s — were sized for the unbalance currents expected from conventional single-phase residential loads, not for the triplen harmonic currents from EV chargers. A neutral conductor that is thermally adequate for 20% residential load unbalance may be significantly overloaded by the triplen harmonic neutral current from 15–20% EV penetration on a feeder end bus.
The practical utility response to EV charging PQ is not primarily technical mitigation — it is data collection. The key unknown for any distribution network is the actual EV penetration on each LV feeder in real time, and the phase distribution of those chargers. A utility that knows which customers on which feeders have EV chargers — and on which phase each charger is connected — has the information needed to identify feeder-end VUF risk before it manifests as a complaint. Without this data, the utility is flying blind. Smart meter data, combined with the probabilistic modelling methodology demonstrated by Torres et al., provides the analytical foundation for proactive LV feeder PQ management in the EV era.
Referências
- Torres S, Durán I, Marulanda A, Pavas A, Quirós-Tortós J. “Electric vehicles and power quality in low voltage networks: Real data analysis and modeling.” Applied Energy, 2021. DOI: 10.1016/j.apenergy.2021.117718
- Iqbal MN et al. “Harmonic and Supraharmonic Emissions of Plug-In Electric Vehicle Chargers.” Smart Cities, vôo. 5, não. 2, pp. 496–524, 2022. DOI: 10.3390/smartcities5020027 — Open access CC BY 4.0.
- Ul-Haq A et al. “Impact of Electric Vehicle Charging on Voltage Unbalance in an Urban Distribution Network.” Intelligent Industrial Systems, vôo. 1, pp. 51–60, 2015.
- IN 50160:2010+A3:2019. Voltage characteristics of electricity supplied by public electricity networks. CENELEC, Bruxelas.
- IEC 61000-3-2:2018. Electromagnetic compatibility — Part 3-2: Limites para emissões de correntes harmônicas. IEC, Genebra.
- IEC 61000-2-2:2002+AMD1:2017. Electromagnetic compatibility — Compatibility levels for low-frequency conducted disturbances in public LV supply systems. IEC, Genebra.
Primary source: Torres S, Durán I, Marulanda A, Pavas A, Quirós-Tortós J. “Electric vehicles and power quality in low voltage networks: Real data analysis and modeling.” Applied Energy, 2021. DOI: 10.1016/j.apenergy.2021.117718. Supporting reference: Iqbal MN et al., “Harmonic and Supraharmonic Emissions of Plug-In Electric Vehicle Chargers,” Smart Cities, 2022, CC BY 4.0.
This case study is presented in summary and commentary form for educational purposes. SVG diagrams and the PQ Perspective section (Seção 6) are original IPQDF editorial content by Denis Ruest, Mestrado. (Aplicado), P.Eng. (ret.). IPQDF does not claim authorship of the original research.