EV Charger Relay Filter Circuit for AC Line EMI Suppression
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Solution Overview
Problem
Existing charging devices for electric vehicles face challenges in minimizing electromagnetic interference (EMI) noise generated by relays, particularly when connected to AC power grids, as conventional filters are inadequate in suppressing relay-related noise.
Innovation Solution
A charging device incorporating a power factor correction (PFC) circuit with inductors and switch legs, a relay network, a relay control circuit, and a relay filter circuit with capacitors to manage relay operations and reduce EMI noise, adaptable to both three-phase and single-phase power sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a relay is applied to the charging device to control power connection, then the charging device can efficiently manage power flow and adapt to different power conditions, but relay power/signal noise is emitted to the AC power line through parasitic capacitance, causing electromagnetic interference
Solution Approach 1:
A relay filter circuit is introduced as an intermediary component between the relay and the AC power line. This filter circuit includes capacitors connected between the AC power line and ground, which act as mediators to block high-frequency noise from propagating to the power line while allowing the relay to continue its normal switching function for efficient power management
2Object-affected harmful factors
If conventional filter circuits are used to suppress EMI noise, then some noise can be filtered, but relay-related noise does not pass through the existing filter circuit, limiting noise suppression performance
Solution Approach 1:
The filter circuit parameters are specifically optimized for relay noise frequencies. Capacitors with appropriate capacitance values are selected to create a low-pass filter characteristic that effectively attenuates the high-frequency relay noise while maintaining proper power transmission. The filter design targets specific frequency ranges where relay noise occurs, changing the electrical parameters to match the noise characteristics
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
The solution effectively minimizes EMI noise, ensuring compliance with ECE-R10 regulations and enhancing charging efficiency and power supply capabilities across various power conditions, including single-phase and three-phase inputs.
Implementation Method 1
a relay filter circuit that includes first to third filter capacitors connected between a ground plane, first to third sensing lines connected to the relay control circuit to sense voltages of the first to third input terminals
Implementation Method 2
noise of a sensing line for controlling the relay are also emitted to an AC power line by a parasitic capacitance
Data Source
AI summary
An embodiment charging device includes a power factor correction circuit first to third switch legs connected to first to third inductors, respectively, a relay network for controlling connection between the first to third inductors and first to third input terminals according to a phase of a power grid connected to the first to third input terminals, a relay control circuit connected to the first to third input terminals for sensing one of the first to third input terminals to which a power source is connected and controlling the relay network based on a sensing result, and a relay filter circuit including first to third filter capacitors connected between a ground plane and first to third sensing lines connected to the relay control circuit for sensing voltages of the first to third input terminals and a fourth filter capacitor connected between the ground plane and a chassis.