Solid State Circuit Breaker Switch with Free-Wheeling Diode
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Solution Overview
Problem
Solid state circuit-breaker (SSCB) switches for hybrid electric vehicles face challenges in achieving low conduction losses, high overload capability, and tolerance for high operating voltages due to issues with current unbalance and thermal stress in MOSFET devices, particularly silicon carbide (SiC) MOSFETs, which can lead to overvoltage spikes and performance degradation during transient conditions.
Innovation Solution
The implementation of a circuit-breaker switch configuration that includes a first solid state switch connected to the positive terminal and a second solid state switch connected to the return terminal, with a free-wheeling diode to limit voltage transients, and a combination of MOSFET and IGBT devices in parallel to manage current and voltage stress, utilizing SiC MOSFETs and silicon-based IGBTs to achieve low conduction losses and high current ratings, along with additional diodes to prevent overvoltage spikes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If SiC MOSFETs are used to reduce conduction losses, then conduction loss is reduced, but overvoltage spikes occur during turn-off events
Solution Approach 1:
A free-wheeling diode is introduced as an intermediary component connected in parallel with the load. During turn-off events, this diode provides a safe path for inductive current to circulate, preventing voltage spikes from damaging the SiC MOSFET while allowing the device to maintain its low conduction loss characteristics
Solution Approach 2:
The patent converts the potentially harmful fast turn-off characteristic of SiC MOSFETs (which causes overvoltage spikes) into a benefit by pairing it with a free-wheeling diode. The diode captures the inductive energy that would otherwise cause damage and redirects it through a safe path, allowing the fast switching capability to be fully utilized without the harmful side effects
2Loss of energy
If MOSFETs are paralleled to achieve desired conduction loss, then conduction loss is reduced, but current unbalance occurs during overload transient conditions
Solution Approach 1:
The patent implements current sensing and control circuitry that continuously monitors the current distribution among parallel MOSFETs. During overload transient conditions, the control system detects current unbalance and adjusts the gate drive signals to redistribute current evenly, preventing any single device from exceeding its ratings
Solution Approach 2:
The patent employs dynamic current sharing control that adapts the operating characteristics of parallel MOSFETs in real-time. During steady-state operation, the devices operate with minimal control intervention, but during transient overload conditions, the control system dynamically adjusts parameters to maintain current balance and prevent device failure
3Speed
If SiC MOSFETs are used for fast turn-off time, then response time is improved, but heat flux increases resulting in higher thermal impedance
Solution Approach 1:
The patent divides the power switching function across multiple parallel MOSFET devices rather than using a single high-power device. This segmentation reduces the current density and heat flux in each individual device, lowering thermal impedance while maintaining the fast turn-off response time through coordinated switching of all devices
Solution Approach 2:
The patent employs advanced thermal management solutions including specialized thermal interface materials and heat sink designs that optimize heat dissipation from the SiC MOSFETs. The composite thermal management system effectively conducts and dissipates the high heat flux generated during fast switching operations
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 configuration provides low conduction losses, high overload tolerance, and reduced overvoltage stress during turn-off events, enabling efficient power management and protection in hybrid electric vehicles, with the ability to withstand up to 1000% overload and high operating voltages, while maintaining low thermal stress and efficient power distribution.
Implementation Method 1
a free-wheeling diode connected between the first and second solid state switches and configured and adapted to limit voltage transients across a load at turn-off conditions
Implementation Method 2
a reverse polarity protection diode connected between the positive terminal and the first solid state switch
Data Source
Figure 1
Figure 2
Figure 3A~3C
AI summary
A solid state circuit-breaker switch (100;200) has a first solid state switch (102) coupled to a positive terminal (12) of a high voltage source, a second solid state switch (104) coupled to a return terminal (14) of the high voltage source, and a diode (18) connected between the switches (102, 104). A load (10) is coupled between the switches (102, 104) and in parallel with the diode (18) such that voltage transients across the load (10) are limited during turn of conditions. Related methods of operating the switch (100;200) during turn-on and turn-off events within rated current operation are described, as are turn-on and turn-off events in overload conditions.