EPS Inverter Bridge Damping Current Suppression
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Solution Overview
Problem
Electric Power Assisted Steering (EPS) systems face issues with damping currents in faulty inverter bridges, which reduce steering assistance and increase heat generation, requiring additional components like blocking switches or relays that occupy space and are expensive.
Innovation Solution
A method to control EPS systems by applying a gate-source voltage to switching elements in affected inverter bridges only when specific conditions are met, such as zero current or current flowing in a safe direction, to prevent damping currents without the need for additional circuit components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If blocking switches or relays are added to prevent damping currents in faulty inverter bridges, then damping currents are suppressed and steering assistance is maintained, but device complexity increases and additional components occupy space and increase cost
Solution Approach 1:
The patent extracts the harmful damping current path by selectively disabling switching elements in the faulty inverter bridge through control signals. Instead of adding blocking components, the solution removes the harmful current circulation path by turning off the relevant switches, thereby preventing damping currents while avoiding additional hardware complexity
Solution Approach 2:
The control system automatically detects faults in inverter bridges and self-regulates by disabling the faulty bridge's switching elements. The system serves itself by monitoring its own state and taking corrective action through control signals, eliminating the need for external blocking components or manual intervention
2Temperature
If blocking switches or relays are installed to prevent damping currents, then heat generation from damping currents is reduced, but the system occupies more space and generates additional heat from the blocking components themselves
Solution Approach 1:
The patent extracts and eliminates the source of excessive heat generation by disabling the faulty inverter bridge's switching elements through control signals. This prevents damping currents and their associated heat without introducing additional heat-generating blocking components into the system
Solution Approach 2:
The patent replaces mechanical blocking switches or relays with electronic control signals that disable the switching elements. This substitution eliminates the need for additional mechanical components that would occupy space and potentially generate heat, using instead a software/control-based solution
3Reliability
If additional blocking components are added to suppress damping currents, then damping current circulation is prevented, but manufacturing cost increases due to more expensive components
Solution Approach 1:
The patent extracts the damping current suppression function from additional hardware components and implements it through control logic that disables switching elements in the faulty inverter bridge. This eliminates the need for expensive blocking switches or relays, reducing manufacturing costs while maintaining reliability
Solution Approach 2:
The existing switching elements in the inverter bridge are made multi-functional by enabling them to operate in both normal power conversion mode and fault isolation mode. The same switches that control motor operation also serve to block damping currents when disabled, eliminating the need for dedicated blocking components and reducing overall system cost
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
Effectively suppresses damping currents, allowing the faulty inverter to be disabled and maintaining steering assistance without the need for additional components, thus reducing heat generation and system failures.
Implementation Method 1
A typical inverter bridge employed in an EPS system comprises a plurality of semiconductor switching elements which control the current delivered to the motor
Implementation Method 2
the generation of a back-EMF (also known as regeneration voltage) within the motor can drive damping currents within the faulty inverter bridge
Implementation Method 3
Common switching elements, for example, MOSFETs, typically have an intrinsic parasitic 'body' diode in parallel to the transistor channel which allows damping currents to circulate
Implementation Method 4
This may be achieved by applying a gate-source voltage to one or more of the switching elements of the affected inverter bridge(s)
Data Source
Figure 1(a)~1(b)
Figure 2
Figure 3
AI summary
A method of controlling an electric power assisted steering (EPS) system comprising one or more inverter bridges each connected to a multi-phase motor configured to provide power assist to steering of a vehicle, wherein each inverter comprises a plurality of switching elements each associated with a phase of the motor, the method comprising in response to detecting a predefined event affecting current flow in one or more of the inverter bridges, preventing current flow in said one or more affected inverters by applying a gate-source voltage to one or more of the switching elements of the affected inverter bridge(s), wherein the switching elements are configured to conduct in the off-state when reverse biased beyond a reverse conduction threshold voltage, and wherein applying the gate-source voltage comprises applying a negative gate-source voltage to control the reverse conduction threshold voltage of the switching elements in the off-state only at a time when there is no current flowing in the direction drain to source through the switching device that exceeds a threshold value.