Pilot Wire Communication During EV Charging PWM Off-States
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Solution Overview
Problem
The existing communication systems on pilot wires in electric vehicles face challenges in maintaining reliable data transmission due to interference from Pulse Width Modulation (PWM) signals, which affect the duty cycle and signal level, limiting the effective impedance and causing distortion and noise interference.
Innovation Solution
The implementation of a pilot wire system with modems that use an interface circuit with a large impedance to prevent distortion, amplify communication signals proportionally to impedance variations, and employ techniques like Orthogonal Frequency-Division Multiplexing (OFDM) or Frequency Shift Keying (FSK) signals, along with a diode to block signals during PWM pulses, ensuring communication only during PWM off-states to preserve signal integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If communication signals are transmitted on the pilot wire during PWM operation, then data communication can be established, but signal distortion and noise interference occur due to PWM signal interference
Solution Approach 1:
The patent extracts the communication function from the power control function by using separate frequency bands. The PWM signals operate at a specific frequency range for power regulation, while communication signals use a different frequency band, allowing both functions to coexist on the same pilot wire without mutual interference.
Solution Approach 2:
The patent segments the frequency spectrum into distinct bands: one for PWM power control signals and another for communication signals. This frequency division allows the pilot wire to simultaneously carry both types of signals by separating them in the frequency domain, thus resolving the interference problem.
2Power
If the impedance of the interface circuit is reduced to improve signal transmission, then signal level increases, but distortion increases due to PWM signal interference
Solution Approach 1:
The patent employs periodic action by using frequency division where communication signals are transmitted during periods when PWM signals are not active, or at different frequencies that do not overlap. This periodic separation in frequency domain prevents the distortion that would occur from direct signal level increases in the presence of PWM interference.
3Productivity
If communication signals are transmitted continuously, then data rate increases, but interference from PWM signals increases causing communication errors
Solution Approach 1:
The patent implements periodic action by transmitting communication signals only during specific time windows or frequency slots that do not overlap with PWM signal activity. This allows continuous communication capability while avoiding periods of PWM interference, maintaining both high data rates and communication accuracy.
Solution Approach 2:
The patent uses dynamic frequency selection or time-division multiplexing where the communication system can dynamically adjust its transmission parameters based on the presence or absence of PWM signals. This dynamic adaptation allows the system to maintain high data rates while avoiding interference-induced errors.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables reliable and high-data-rate communication on pilot wires by maintaining signal integrity and overcoming noise and interference, allowing for efficient power management and communication between Electric Vehicle Supply Equipment (EVSE) and Electric Vehicles (EVs), even in noisy environments.
Implementation Method 1
The interface circuit includes a diode that blocks the first modem communication signals from reaching the pilot wire when a PWM pulse is present on the pilot wire. The diode comprises an anode coupled to the first modem and a cathode coupled to the pilot wire. The diode conducts the first modem communication signals to the pilot wire when the PWM signals are off.
Implementation Method 2
The line driver circuit in the interface circuit amplifies the communication signals prior to injection onto the pilot wire. The line driver circuit amplifies the communication signals by an amount proportional to a variation in the effective impedance of the pilot wire system, wherein the effective impedance variations are caused by the PWM signals changing from an on-state to an off-state.
Data Source
AI summary
Systems and methods are disclosed for communicating on a pilot wire between Electric Vehicle Service Equipment (EVSE) and an Electric Vehicle (EV). The EVSE and EV exchange a Pulse Width Modulation (PWM) signal on the pilot wire to control charging operations of the EV. Data communications may also be transmitted on the pilot wire, such as between transmit and receive modems. The modems transmit communication signals either continuously, without regard to the state of the PWM signal, or only when the PWM is in an off-state. If transmitting while PWM is on, the modem needs a large coupling impedance and/or a large signal injection. To transmit only when the PWM is off, the modem may use a blocking diode in the coupling circuit or may synchronize to the pulses in the PWM signal.