High Frequency Injection for HV Interlock Detection
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Solution Overview
Problem
Existing systems for detecting cable connections between electric machines and power inverters in hybrid-electric vehicles require additional connectors or conductors, increasing complexity and cost, and lack reliable methods for detecting connection status without extensive calibration.
Innovation Solution
A method involving a controller that applies a diagnostic injection current with a frequency multiple of the switching frequency to the electric machine, allowing for the detection of connection status without additional connectors, by measuring the difference between the injection current and the measured current, and using discrete Fourier transform to determine sequence voltages, thereby identifying a loss of connection diagnostic.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional low-voltage signal lines are included to monitor connection status, then connection detection capability is improved, but device complexity increases
Solution Approach 1:
The existing three-phase conductors used for power transmission are made to serve a dual function: they transmit power during normal operation and carry diagnostic injection currents for connection status monitoring. This eliminates the need for separate dedicated signal lines, resolving the contradiction by making the existing infrastructure multi-functional.
Solution Approach 2:
The diagnostic monitoring function is merged with the power transmission function by using the same physical conductors for both purposes. The injection current shares the pathway with the main power current, combining two functions into one physical infrastructure and eliminating additional hardware.
2Reliability
If high magnitude injection current is used for detection, then detection reliability is improved, but safety concerns increase
Solution Approach 1:
Instead of using full-power high-magnitude currents for detection, the system employs partial action by injecting small-magnitude diagnostic currents that are sufficient for reliable detection but too small to pose safety risks. The detection function achieves adequate reliability without the excessive current magnitude that would create harmful effects.
Solution Approach 2:
The injection current is applied periodically at specific frequencies (predetermined multiples of switching frequency) rather than continuously. This periodic injection at controlled intervals allows reliable detection while limiting the total energy exposure and maintaining safety, as the small-magnitude current is only present during brief diagnostic intervals.
3Reliability
If traditional connection monitoring methods are used, then connection status can be monitored, but extensive calibration is required
Solution Approach 1:
The system performs self-diagnosis by injecting currents at predetermined frequencies and analyzing the resulting voltage responses. The controller automatically compares measured sequence voltages against predetermined thresholds without requiring external calibration equipment or manual adjustment, making the system self-sufficient and eliminating extensive calibration requirements.
Solution Approach 2:
The system changes the frequency parameter of the injection current to predetermined multiples of the switching frequency, which creates distinct voltage responses that can be easily distinguished and analyzed. This parameter selection simplifies the detection process and eliminates the need for extensive calibration, as the predetermined frequencies naturally produce measurable differential responses.
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 enables reliable detection of connection presence or absence without additional hardware, reduces safety concerns due to small injection current magnitude, and does not require extensive calibration, simplifying the detection process.
Implementation Method 1
A power inverter includes at least one controller programmed to apply a voltage to an electric machine corresponding to an injection current... The predetermined sequence voltages may be based on an inductance of the electric machine
Implementation Method 2
The sequence voltages may be based on a discrete Fourier transform of the voltage
Data Source
AI summary
A power inverter for driving an electric machine is configured to apply a voltage to the electric machine based on a high-frequency injection current. Three phase currents are measured and input into a current controller. A voltage command output from the current controller is monitored using a discrete Fourier transform to determine a positive and negative sequence voltage of the voltage command. The sequence voltages are compared to expected positive and negative sequence voltages. A loss of connection diagnostic is output if a magnitude of the difference between the expected and actual sequence voltages is greater than a predetermined threshold.