PWM-Driven MOSFET Linear Control for Low-EMI Heated Seats
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Solution Overview
Problem
Existing power MOSFET systems in switching applications, such as electric vehicle seat heaters, generate high electromagnetic emissions and interference, often exceeding safety guidelines, particularly during turn-on and turn-off of resistive loads.
Innovation Solution
The system and method involve operating the power MOSFET in its Ohmic region through pulse-width-modulated (PWM) control voltage, adjusting the frequency and duty cycle to minimize electromagnetic fields without requiring a dedicated DC/DC converter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a power MOSFET operates in switching mode to control heat mat power, then power regulation efficiency is improved, but electromagnetic emissions exceed safety guidelines
Solution Approach 1:
The patent changes the operating parameters of the MOSFET from conventional switching mode to linear mode operation. By adjusting the gate-source voltage to maintain the MOSFET in its ohmic region and using pulse-width modulation to control the duty cycle, the system achieves effective power regulation while keeping electromagnetic emissions below ICNIRP guidelines, particularly during turn-on and turn-off transitions
Solution Approach 2:
The patent employs pulse-width-modulated periodic gate voltage signals to control the MOSFET. By applying periodic pulses with adjusted duty cycles rather than continuous switching, the system regulates power to the heat mat while limiting the rate of change of current (di/dt) and voltage (dv/dt), thereby reducing electromagnetic radiation during each switching cycle
2Use of energy by moving object
If the heat mat resistance is lowered at lower temperatures, then heating efficiency is improved, but electromagnetic emissions increase
Solution Approach 1:
The patent incorporates feedback control by monitoring the actual current through the heat mat and adjusting the MOSFET gate voltage accordingly. This feedback mechanism ensures that even when heat mat resistance decreases at lower temperatures, the system maintains electromagnetic emissions within safe limits by dynamically controlling the MOSFET operating point and pulse width
Solution Approach 2:
The system dynamically adjusts operating parameters including gate voltage magnitude, pulse width, and frequency based on the heat mat's instantaneous resistance. By adapting these parameters in real-time, the system maintains efficient heating while preventing electromagnetic emissions from exceeding guidelines during temperature transitions
3Object-generated harmful factors
If a dedicated DC/DC converter is used to reduce electromagnetic field, then electromagnetic emissions are reduced, but cost, size, and weight increase
Solution Approach 1:
The patent makes the power MOSFET perform multiple functions: it serves as both the power switching element for heat mat control and the electromagnetic emission mitigation device. By operating the MOSFET in linear mode with pulse-width modulation, it achieves emission reduction without requiring a separate DC/DC converter, thereby reducing overall system complexity, cost, and component count
Solution Approach 2:
The patent merges the power control function and electromagnetic emission control function into a single MOSFET device. Instead of using separate components for power regulation and emission filtering, the system combines these functions by strategically operating the MOSFET in its ohmic region with controlled pulse-width modulation, eliminating the need for additional emission-reduction hardware
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 significantly reduces electromagnetic interference, with emissions during turn-on and turn-off being only 77% and 65% of ICNIRP guidelines, respectively, while also reducing start-up current for heat mats at lower temperatures.
Implementation Method 1
operating the power MOSFET in its Ohmic region
Implementation Method 2
a heat mat for converting electrical energy into heat. The heat mat includes a resistive heating element
Implementation Method 3
The frequency and the duty cycle of the PWM gate voltage (V GS ) are iteratively selected such that the power MOSFET operates only in its Ohmic region
Implementation Method 4
Additional embodiments include winding the heater coil in a first direction and in a second, opposite direction, such that the magnetic field is canceled along the length of the heater coil
Data Source
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AI summary
A system and a method for controlling a power MOSFET for limiting electromagnetic interference from a load is provided. The system and method include a pulse-width-modulated (PWM) control voltage to operate the power MOSFET in accordance with its Ohmic region (linear mode). By operating the power MOSFET in its Ohmic region, the electromagnetic field generated by the load is reduced, without requiring a dedicated DC/DC converter that would otherwise increase the cost, size, and weight of the power electronics.