High-Frequency Signal Injection for HV Cable Connectivity Detection
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Solution Overview
Problem
Existing methods for determining high voltage cable connectivity in electric vehicles, such as mechanical switches and current comparison methods, are unreliable and prone to false alarms, especially during low torque operations, and can cause noise vibration harshness (NVH) issues.
Innovation Solution
An electronic system that injects a high frequency signal over the fundamental command voltage to determine the high frequency current component values, using a strategy determination module to select an appropriate fault detection strategy based on motor operational modes, and a fault detection module to assess cable connectivity by analyzing positive and negative sequence component values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mechanical interlock switch is used to detect cable connectivity, then the system can determine connectivity status, but the reliability deteriorates due to mechanical degradation and failure
Solution Approach 1:
The patent replaces the mechanical interlock switch with an electronic high-frequency signal injection method. The system injects a high-frequency signal through the power conversion circuit and detects the resulting current response to determine cable connectivity. This eliminates mechanical moving parts, contacts, and switches, thereby improving reliability while reducing mechanical complexity.
Solution Approach 2:
The system uses the motor's own electrical characteristics and existing power conversion circuitry to perform the connectivity detection. The high-frequency signal is injected through the same power conversion circuit that drives the motor, and the current response is measured using the existing current sensors. This self-service approach eliminates the need for separate mechanical detection devices.
2Measurement precision
If actual stator currents are compared to estimated stator currents to determine connectivity, then connectivity status can be detected, but false alarms increase during low torque operation
Solution Approach 1:
The patent employs periodic high-frequency signal injection at specific intervals during motor operation. By injecting the signal periodically and analyzing the current response at known frequencies, the system can distinguish between normal operational variations and actual connectivity faults. This periodic action reduces false alarms during low torque operation where current comparisons are particularly susceptible to errors.
Solution Approach 2:
The system changes the detection parameter from low-frequency current comparison to high-frequency signal response analysis. By using a high-frequency signal (typically above 1 kHz), the system exploits the electrical characteristics of the cable and motor at these frequencies to determine connectivity. This parameter change makes the detection less sensitive to torque-related current variations that cause false alarms in traditional methods.
3Reliability
If a pulsed current method is used to indicate connectivity during low torque operation, then false alarms are reduced, but noise vibration harshness problems increase
Solution Approach 1:
The patent changes the detection signal from a pulsed current injection to a high-frequency sinusoidal signal injection. The sinusoidal signal at high frequencies produces minimal audible noise and vibration compared to pulsed current methods. The system analyzes the magnitude and phase of the current response at the injection frequency to determine connectivity, achieving reliable detection during low torque operation without significant NVH penalties.
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 provides reliable and efficient detection of high voltage cable connectivity with minimal false alarms and reduced NVH, effectively enabling system shutdown when open phases are detected, thus ensuring safe operation of electric vehicles.
Implementation Method 1
An example system can be configured to superimpose a high frequency signal over a fundamental command voltage, determine a high frequency current component value, and perform a fault detection function using the high frequency current component value.
Data Source
AI summary
Systems, methods and apparatus are presented to determine high voltage cable connectivity between an inverter module and a remote electric machine. A high frequency (HF) interlock module can be configured to inject a high frequency excitation signal that can be superimposed on inverter drive signals. High frequency current components can be determined and used to determine connectivity status. The sum and difference of positive and negative sequence component values can be compared to predetermined limitations to detect one or more open phases. An example method can include enabling a HF detection strategy under predetermined conditions. In response to an open phase detection a fault flag can be set.