GaN Transistor Isolation Switches for Multi-Phase Motor Control
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Solution Overview
Problem
Existing control circuits for multi-phase motors using MOSFETs for phase isolation face issues with unwanted damping currents due to the intrinsic body diode, leading to reduced steering assistance in electric power assisted steering systems, and require a high number of costly MOSFETs to control these currents effectively.
Innovation Solution
The use of Gallium Nitride (GaN) transistors as isolation switches in the control circuit reduces the number of components needed for phase isolation, eliminating the need to compensate for the body diode, thereby reducing energy consumption and heat evolution, and allows for selective isolation of output voltage to prevent uncontrolled currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If MOSFETs are used for phase isolation, then current control in one direction is achieved, but unwanted damping currents occur due to the intrinsic body diode
Solution Approach 1:
The patent extracts and removes the parasitic body diode function from the isolation switch by using a GaN HEMT transistor instead of a MOSFET. The GaN transistor provides the necessary current blocking capability without the unwanted reverse conduction path that causes damping currents, thereby eliminating the harmful effect while maintaining the isolation function.
Solution Approach 2:
The patent changes the material parameter from silicon-based MOSFET to gallium nitride-based HEMT transistor. This material parameter change fundamentally alters the device characteristics, eliminating the body diode effect and enabling unidirectional current blocking without the parasitic reverse conduction that plagues MOSFET-based isolation switches.
2Reliability
If 3 or 4 MOSFETs are used per phase for full current control, then unwanted currents are controlled, but component count and cost increase significantly
Solution Approach 1:
The patent extracts the problematic body diode function from the isolation switch architecture, allowing a single GaN transistor to perform the isolation function that previously required multiple MOSFETs. This extraction of the parasitic element enables a much simpler circuit topology with fewer components while maintaining full current control capability.
Solution Approach 2:
By changing the transistor type from MOSFET to GaN HEMT, the patent fundamentally changes the device parameters to eliminate the body diode effect. This parameter change allows a single transistor to provide the isolation function, reducing the component count from 3-4 MOSFETs per phase to just one GaN transistor per phase.
3Reliability
If multiple MOSFETs are used for phase isolation, then current control is improved, but energy losses and heat evolution increase
Solution Approach 1:
The patent changes the material parameter from silicon-based MOSFET to gallium nitride-based HEMT transistor, which fundamentally alters the energy loss characteristics. GaN transistors exhibit lower on-resistance and eliminate body diode conduction losses, resulting in significantly reduced inserted losses and heat evolution while maintaining effective current control.
4Reliability
If MOSFETs are used for isolation, then phase isolation function is achieved, but steering assistance is reduced due to damping currents
Solution Approach 1:
The patent extracts and removes the body diode conduction path from the isolation switch, eliminating the source of damping currents that reduce steering assistance. By using a GaN HEMT transistor instead of a MOSFET, the harmful reverse conduction is removed while the forward isolation function is maintained, preserving steering assistance.
Solution Approach 2:
The patent changes the device material from silicon MOSFET to gallium nitride HEMT, which fundamentally changes the electrical parameters to eliminate body diode effects. This parameter change removes the harmful damping currents that degrade steering assistance while maintaining the necessary phase isolation function.
Data Source
AI summary
A control circuit for a multi-phase motor (57) comprises a plurality of inverter bridges, a plurality of outputs, and at least one isolation switch (62, 63). Each inverter bridge is arranged to provide an output voltage for a phase of the motor (57). Each output is arranged to be coupled to one phase of the motor (57) to provide the output voltage to that phase of the motor (57). Each isolation switch (62, 63) is coupled between one of the inverter bridges and one of the outputs, so as to selectively isolate the output from the inverter bridge. Each isolation switch (62, 63) comprises a Gallium Nitride (GaN) transistor.