Electronics Guide

Emission Sources and Characteristics

DWC roadway infrastructure generates emissions from multiple sources:

Transmitter coils: The primary power transmission coils, typically operating in the 20-150 kHz range for automotive applications, generate strong magnetic fields at the fundamental frequency. Field intensity varies depending on power level, typically ranging from 3 kW for light vehicles to 200 kW or more for heavy-duty applications.

Power conversion equipment: Grid-tie inverters and DC-DC converters create conducted emissions on utility connections and radiated emissions from power cabinets. Switching frequencies typically range from tens of kilohertz to hundreds of kilohertz.

Harmonic emissions: Non-sinusoidal drive waveforms generate harmonics extending to tens of megahertz. Harmonic content depends on inverter topology, switching frequency, and filter design.

Control and communication systems: Wireless communication for vehicle detection, authentication, and power control generates additional emissions at communication frequencies (typically 2.4 GHz or other ISM bands).

Spatial Distribution

Roadway emissions have distinctive spatial characteristics:

In-roadway fields: Within the charging lane, field intensity is sufficient for power transfer, typically hundreds of microtesla to several millitesla. These fields must be contained to minimize exposure to adjacent lanes and roadside areas.

Roadside exposure: Pedestrians, cyclists, and occupants of adjacent non-charging vehicles experience fields that decrease with distance from the charging lane. Field levels at accessible locations must comply with exposure limits.

Above and below roadway: Fields extend both above the road surface (into the vehicle charging space) and below (into infrastructure tunnels and utility corridors). Subsurface utility equipment may require protection from magnetic field exposure.

Along-road variation: As vehicles move along the charging lane, different transmitter coils activate sequentially. This creates a traveling field pattern with intensity variations along the road.

Emission Control Strategies

Managing roadway emissions employs multiple approaches:

Segmented coil design: Rather than energizing long stretches of roadway continuously, segmented systems activate individual coil segments only when a vehicle is present. This dramatically reduces the active field extent and total emissions.

Shielding integration: Ferrite and conductive shielding integrated into the roadway structure contains fields to the charging region. Shield design must balance EMC performance against cost, weight, and durability requirements.

Coil topology optimization: DD (double-D), DDQ, and other advanced coil topologies create field patterns with improved coupling efficiency and faster field decay with distance compared to simple circular coils.

Power management: Reducing power when vehicles are not present or when full power is not needed minimizes emissions. Intelligent power control responds to vehicle demand and position.

Filtering: Input and output filters reduce conducted emissions to the utility grid and harmonic content of the transmitted field.

Measurement Challenges

Characterizing DWC roadway emissions presents unique measurement challenges:

• Large scale: Charging lanes may extend hundreds of meters or more, requiring extensive measurement campaigns to characterize emissions along the full installation
• Dynamic operation: Emissions vary with vehicle presence, position, and power demand. Static measurements may not capture worst-case conditions
• Environmental factors: Road surface moisture, temperature, and nearby vehicle traffic affect measurement conditions
• Access limitations: Active roadway installations may have limited access for measurement during normal operation
• Background noise: Roadway environments have high ambient electromagnetic noise from vehicle ignition systems, electronic controls, and communication devices

Detection Technologies

Various technologies enable vehicle detection for DWC:

Magnetic sensing: Changes in the magnetic field pattern caused by vehicle presence (through ferromagnetic vehicle components and onboard receiver coils) can trigger coil activation. Existing inductive loop detectors used for traffic management may be adapted for DWC detection.

Radio communication: Direct communication between vehicle and infrastructure via dedicated short-range communication (DSRC), cellular V2X, or dedicated DWC protocols enables identification and position reporting.

Radar sensing: Roadside or in-pavement radar can detect and track vehicles regardless of their electronic equipment, providing redundancy and detecting non-equipped vehicles.

Optical sensing: Camera systems with image processing can identify vehicles and track position, though performance may degrade in adverse weather conditions.

GNSS position: Vehicle-reported GPS position can guide coil activation, though accuracy limitations may require supplementation with local positioning systems.

Detection System EMC

Vehicle detection systems must achieve EMC with the DWC power system:

Immunity to power fields: Detection sensors operating near active power coils experience strong magnetic fields at the power transfer frequency. Sensors must reject this interference while maintaining sensitivity to detection signals.

Communication reliability: Radio communication for detection must work reliably despite the electromagnetic environment created by power transfer. Frequency selection, modulation robustness, and error correction are critical.

False detection management: Detection systems must distinguish authorized DWC vehicles from other vehicles, metallic road debris, or electromagnetic anomalies to prevent false coil activation.

Detection system emissions: Active detection systems (radar, communication links) generate their own emissions that must comply with applicable regulations.

Timing and Coordination

Detection system timing is critical for DWC operation:

Anticipatory detection: Coils must activate before the vehicle arrives to allow power transfer system startup. Detection range must extend upstream of each charging segment.

Handoff coordination: As vehicles move between segments, detection must coordinate the deactivation of trailing segments and activation of leading segments to maintain continuous charging.

High-speed operation: At highway speeds, vehicles traverse coil segments in fractions of a second, requiring rapid detection response and communication latency in milliseconds.

Multi-lane coordination: Detection systems must track vehicles across multiple lanes and handle lane changes during charging.

Position Variation Sources

Several factors cause position variation in DWC:

Lane position: Vehicles naturally wander within their lane during normal driving. Lane position variation of plus or minus 20-30 cm is typical for unguided driving; automated lane-keeping may reduce this but not eliminate it.

Vehicle height: Suspension deflection, load variation, and road surface irregularities cause the vehicle-mounted receiver to move vertically. Height variation of several centimeters is common.

Pitch and roll: Vehicle attitude changes during acceleration, braking, and cornering tilt the receiver relative to the road surface, affecting coupling geometry.

Road irregularities: Bumps, dips, and surface variations cause transient position changes that affect instantaneous coupling.

Vehicle-to-vehicle variation: Different vehicle models have different receiver mounting heights and positions, creating system-level position variation.

EMC Implications of Position Variation

Position variation affects EMC through several mechanisms:

Coupling variation: As position varies, coupling efficiency changes, requiring power level adjustment to maintain output. The range of power adjustment affects both efficiency and emissions.

Field pattern changes: Misaligned operation creates asymmetric field patterns that may increase emissions in some directions while decreasing them in others.

Detuning: Position-dependent coupling variation causes detuning in resonant systems, potentially shifting operating frequency or reducing efficiency.

Worst-case emissions: EMC compliance must consider the position that creates maximum emissions, which may not be the same as the position of best efficiency.

Design for Position Tolerance

DWC systems employ various approaches to achieve position tolerance:

• Extended transmitter coils: Transmitter coils wider than the receiver provide consistent coupling across the range of lateral positions
• Multiple coil segments: Parallel coil segments can be selectively activated based on vehicle position, optimizing coupling for the actual position
• DD and DDQ receiver coils: Advanced coil topologies provide better lateral tolerance than circular coils
• Adaptive power control: Real-time power adjustment maintains desired charging rate across position variations
• Vehicle guidance: Lane markings, automatic steering assistance, or dedicated guideways reduce position variation

Control Requirements

DWC power control must address multiple requirements:

Vehicle demand: Different vehicles have different power acceptance capabilities and charging needs. Power levels from 3 kW for passenger vehicles to 200+ kW for heavy trucks must be supported.

Position compensation: As coupling varies with position, power drive must adjust to maintain desired receiver power output.

Speed adaptation: Faster vehicles traverse charging segments more quickly, requiring higher instantaneous power to achieve the same energy transfer.

Battery state: Vehicle battery state of charge and temperature affect acceptable charging rate, requiring power reduction in some conditions.

Grid constraints: Utility capacity and power quality requirements may limit total power available at any time.

Control System Architecture

DWC power control typically involves multiple levels:

Segment-level control: Each charging segment has local control that manages power delivery based on vehicle presence and position. Response time must be fast enough to track rapid position changes.

Zone-level coordination: Groups of segments coordinate to manage power sharing, handoffs between segments, and aggregate power demand.

System-level management: Central systems manage grid interaction, demand response, and coordination with traffic management systems.

Vehicle-infrastructure communication: Bidirectional communication enables the vehicle to report its capabilities and charging needs while the infrastructure reports available power and charging status.

EMC Effects of Power Control

Power control activities influence EMC characteristics:

Power transients: Rapid power changes during segment handoffs or position compensation create transient emissions that may exceed steady-state levels.

Control loop dynamics: Power control feedback loops can create oscillations or instabilities that modulate emissions, potentially creating sideband emissions around the operating frequency.

Maximum power operation: Peak power conditions, though perhaps infrequent, may create worst-case emissions that must be considered for compliance.

Reduced power benefits: Power back-off during light-load operation reduces emissions proportionally, potentially providing significant emission reduction during non-peak operation.

Multi-Vehicle Scenarios

Various multi-vehicle situations arise in DWC operation:

Platoon charging: Multiple vehicles traveling in close formation (platooning) may all require charging simultaneously. The close spacing concentrates power demand and field sources.

Multi-lane operation: Adjacent charging lanes may serve vehicles simultaneously, with potential for electromagnetic interaction between lanes.

Mixed traffic: Non-charging vehicles (conventional vehicles, non-equipped EVs) traveling in or adjacent to charging lanes experience fields from active charging without benefiting from power transfer.

Variable speed: Vehicles at different speeds overtaking or being overtaken in charging lanes create time-varying multi-vehicle configurations.

Electromagnetic Interactions

Multiple simultaneous charging events create complex EMC situations:

Field superposition: Fields from multiple active transmitter segments add vectorially. Depending on phase relationships, this can create regions of enhanced or reduced field intensity.

Cross-coupling: Vehicle receivers may couple to transmitters intended for other vehicles, creating unintended power transfer paths and potential efficiency loss.

Inter-vehicle coupling: Adjacent vehicles' receivers may couple to each other, creating additional electromagnetic interactions.

Power sharing: Total system power capability may be shared among multiple vehicles, requiring power management strategies when demand exceeds capacity.

Design Considerations

Managing multi-vehicle effects requires:

• Segment isolation: Physical and electrical design that minimizes coupling between adjacent segments and lanes
• Phase coordination: Controlling phase relationships among adjacent active segments to avoid constructive interference in unintended locations
• Power allocation: Algorithms that fairly and efficiently allocate available power among multiple vehicles
• Cross-coupling rejection: Receiver designs that reject power from unintended transmitter segments
• EMC compliance across scenarios: Verification that EMC limits are met under realistic multi-vehicle operating conditions, not just single-vehicle cases

Utility Grid Interface

DWC systems connect to the electrical utility grid:

Power quality: High-power rectifiers and inverters can inject harmonic currents into the grid, affecting power quality for other utility customers. Standards such as IEEE 519 specify limits on harmonic injection.

Conducted emissions: Switching noise from power electronics can propagate through utility connections. Input filters must attenuate these emissions to meet conducted emission limits.

Grid stability: Large DWC installations represent variable loads that can affect local grid stability. Coordination with utility operators may be required for installations above certain power levels.

Power factor: Maintaining high power factor reduces current draw for a given power level and minimizes impact on utility infrastructure.

Roadway Systems Compatibility

DWC must coexist with other roadway electronic systems:

Traffic management: Inductive loop vehicle detectors, traffic signals, and changeable message signs operate in the roadway environment. DWC fields must not interfere with these systems.

Toll collection: Electronic toll collection systems (RFID-based) may operate near DWC lanes. Frequency coordination prevents interference.

Vehicle communication: V2X (vehicle-to-everything) communication systems share the roadway environment with DWC. Spectrum management ensures coexistence.

Emergency systems: Emergency vehicle preemption, roadway sensors for weather and incident detection, and emergency communication systems must remain operational.

Underground Utilities

DWC infrastructure interacts with subsurface utilities:

Metallic pipelines: Metal gas, water, and sewer pipes beneath the roadway may couple to DWC fields. Induced currents can cause corrosion or interfere with cathodic protection systems.

Communication cables: Buried fiber optic and copper communication cables may be affected by strong magnetic fields. Metal sheaths can couple to fields; even fiber optic cables may have metallic strength members or shields.

Electrical conduits: Underground power distribution and street lighting circuits may couple to DWC fields through common ground connections or direct field coupling.

Adjacent Land Use

DWC installations may affect neighboring properties:

• Residential exposure: Homes near DWC roadways may experience elevated field levels. Exposure assessment must consider occupied spaces in adjacent buildings
• Commercial and industrial: Nearby businesses may have sensitive equipment affected by DWC emissions. Manufacturing facilities, medical offices, and data centers may require specific attention
• Agricultural: Farm equipment, livestock identification systems, and irrigation controllers near rural DWC installations may require evaluation

Energy Measurement

Accurate energy measurement is essential for billing:

Measurement location: Energy can be measured at the grid connection, at each segment, or at the vehicle receiver. Each approach has accuracy and implementation implications.

Efficiency accounting: Power delivered to the vehicle is less than power drawn from the grid due to system losses. Billing may be based on grid energy, delivered energy, or negotiated efficiency factors.

Dynamic measurement: With vehicles moving and power levels varying rapidly, energy measurement must integrate accurately over short intervals and aggregate across multiple segments.

Measurement accuracy: Revenue-grade metering requires accuracy typically better than 1-2%. Achieving this accuracy in the DWC electromagnetic environment is challenging.

Communication for Billing

Billing requires reliable data communication:

Vehicle identification: Secure identification of the charging vehicle prevents billing fraud and enables account association. Authentication must be robust against interference and spoofing.

Usage data transfer: Energy usage data must be transferred from roadway infrastructure to billing systems. Communication reliability affects billing accuracy and dispute resolution.

Real-time capability: Some billing models require real-time communication to verify vehicle authorization and account status before charging.

EMC Considerations for Billing Systems

Billing system EMC requirements include:

• Meter immunity: Energy meters must maintain accuracy despite strong ambient magnetic fields from power transfer. Shielding and appropriate meter placement are essential
• Communication immunity: Billing communication links must resist interference from DWC power systems. Error detection and retransmission protocols handle occasional communication errors
• Tamper resistance: EMI could potentially be used to interfere with metering or billing communication. Systems should be resistant to such attacks
• Audit capability: Recorded data must support verification and dispute resolution, requiring reliable storage and retrieval in the roadway environment

Safety Hazards

DWC systems present several potential hazards:

Human exposure: Pedestrians, road workers, or accident victims in charging lanes may be exposed to strong magnetic fields. Exposure levels in accessible areas must comply with limits, and systems should detect and respond to human presence.

Foreign object heating: Metal debris in charging lanes (dropped cargo, vehicle parts, coins, tools) can heat in the magnetic field, potentially causing fires or burns.

Electrical hazards: High-voltage power systems create shock hazards if insulation is compromised by road damage, water intrusion, or equipment failure.

Vehicle malfunctions: Failures in vehicle charging systems could create hazardous conditions requiring infrastructure response.

Interlock Systems

Multiple interlock systems protect against hazards:

Foreign object detection: Sensors detect metallic objects on the road surface over transmitter coils. Detection triggers power shutdown or reduction before hazardous heating occurs.

Live object protection: Systems detect the presence of humans or animals in charging areas. Detection sensitivity must distinguish safety-relevant living objects from vehicles and road debris.

Ground fault protection: Electrical faults that could energize accessible surfaces are detected and cleared rapidly.

Communication-based interlocks: Loss of communication with vehicles or central systems triggers safe shutdown.

Emergency stop: Manual emergency stop provisions allow rapid system shutdown by road workers or emergency responders.

Safety System EMC Requirements

Safety interlock systems have stringent EMC requirements:

Immunity: Safety systems must operate correctly despite the strong electromagnetic environment created by DWC power systems. False trips reduce system availability; failure to trip creates safety risk.

Reliability: Safety systems must achieve high reliability, typically specified in terms of safety integrity level (SIL) or performance level (PL). EMI-induced failures count against reliability targets.

Diagnostic coverage: Systems must detect their own failures, including failures caused by electromagnetic interference. Self-test and monitoring functions verify continued operation.

Redundancy: Critical safety functions may require redundant sensors or logic to achieve required reliability. Redundant systems must have independence from common-mode EMI failures.

Response time: Safety systems must respond within specified times to prevent hazardous conditions. EMI-induced delays must be accounted for in timing analysis.

Exposure Scenarios

Various exposure scenarios must be considered:

Vehicle occupants: Occupants of charging vehicles are exposed to fields within the vehicle cabin. Vehicle body shielding typically reduces interior field levels significantly below external levels.

Non-charging vehicle occupants: People in conventional vehicles or non-equipped EVs traveling in or adjacent to charging lanes experience exposure without the benefit of optimized receiver positioning.

Pedestrians: People walking near charging lanes (sidewalks, crosswalks, stopped at signals) may be exposed. Children and wheelchair users may be closer to ground level where fields are stronger.

Road workers: Maintenance personnel working on or near charging lanes may have prolonged exposure. Occupational exposure limits may apply to these workers.

Accident scenarios: Vehicle accidents in charging lanes may place occupants or responders in close proximity to active transmitters.

Exposure Assessment

Comprehensive exposure assessment requires:

Field mapping: Detailed measurement or simulation of field strength throughout the accessible environment, including at ground level, standing adult height, and intermediate heights.

Worst-case analysis: Identifying operating conditions that create maximum exposure, including maximum power operation, specific vehicle positions, and multi-vehicle scenarios.

Time averaging: Exposure standards typically allow time averaging. The transient nature of DWC exposure (vehicles pass charging zones in seconds) may allow higher instantaneous fields than would be permitted for continuous exposure.

Population considerations: General public limits protect all population groups including potentially sensitive individuals. Specific scenarios involving medical implant users may require additional analysis.

Exposure Mitigation

Strategies for managing public exposure include:

• Coil design: Optimized coil topologies that concentrate fields in the coupling region while minimizing field extension to accessible areas
• Shielding: Conductive and magnetic shielding integrated into road structure to reduce fields at pedestrian locations
• Separation: Routing charging lanes away from pedestrian areas where possible; providing buffers between charging infrastructure and sidewalks
• Segmented operation: Activating only the coil segments needed for current vehicles, reducing total active field sources
• Power management: Operating at minimum necessary power levels reduces exposure proportionally
• Signage and barriers: Warning signs and physical barriers to prevent public access to highest-field areas

Medical Device Considerations

People with implanted medical devices require special consideration:

Pacemakers and ICDs: Cardiac rhythm management devices may be affected by strong magnetic fields. The devices may inhibit pacing, trigger inappropriate therapy, or experience programming changes.

Insulin pumps: Some insulin pumps have magnetic field sensitivity that could affect operation.

Cochlear implants: Hearing implants may experience interference or demagnetization of internal magnets.

Other implants: Neurostimulators, drug pumps, and other active implants have varying magnetic field sensitivity.

Assessment should verify that field levels in accessible areas do not exceed medical device manufacturer specifications or general EMC immunity standards for medical electrical equipment.