Inverter Operating State Circuit for Electric Machine Safety
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Solution Overview
Problem
Existing inverter systems for electric vehicles with synchronous machines face challenges in safely managing faults, particularly in ensuring safety for emergency services and electrical system integrity during low-voltage side failures, as they either lead to high braking torque at low speeds or excessive charging currents at high speeds, potentially damaging power electronics.
Innovation Solution
An inverter arrangement with a control system that determines the pole wheel frequency independently of position sensors to switch between freewheeling and active short-circuit states based on speed thresholds, optimizing safety by avoiding speed-dependent disadvantages and self-supplying energy during faults.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the inverter is set to active short circuit at low speeds, then safety for emergency services and electrical system integrity is improved, but high braking torque occurs on the shaft of the electrical machine
Solution Approach 1:
The patent applies dynamics by making the safe operating state variable rather than fixed. The control device dynamically selects between freewheeling state and active short circuit state based on the instantaneous speed of the electrical machine. At low speeds, the freewheeling state is selected to avoid high braking torque, while at high speeds, the active short circuit state is selected to prevent excessive charging currents. This dynamic adaptation resolves the contradiction between safety and braking torque.
2Force
If the inverter is set to freewheeling state at high speeds, then high braking torque is avoided, but excessive charging currents occur that can damage power electronics
Solution Approach 1:
The control device dynamically adjusts the safe operating state based on speed conditions. When speed exceeds a predetermined threshold, the system transitions from freewheeling state to active short circuit state, preventing excessive charging currents that would damage power electronics. This dynamic switching resolves the contradiction between avoiding braking torque and preventing harmful charging currents.
3Measurement precision
If position sensors are used to determine speed, then accurate speed detection is achieved, but device complexity and cost increase
Solution Approach 1:
The system uses the electrical machine's own operating parameters (phase currents and voltages) to determine its speed through evaluation of the pole wheel frequency. This self-service approach eliminates the need for external position sensors, reducing device complexity and cost while maintaining sufficient accuracy for safe operating state determination. The evaluation device calculates speed from existing electrical signals rather than requiring separate measurement components.
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
The solution effectively sets safe operating states for the inverter, preventing high braking torque at low speeds and excessive charging currents at high speeds, thereby enhancing the safety and integrity of the electrical machine and control electronics.
Implementation Method 1
the evaluation device (6) is designed to detect the pole wheel voltage (U_PN) present at the phase connections (4a, 4b, 4c) independently of a position detection of the pole wheel of an electrical machine (5) by position sensors
Implementation Method 2
the induced rotor voltage is transmitted via the diodes of the switching devices of the inverter (3) is fed back into the intermediate DC circuit
Data Source
Figure 1
Figure 2~3
AI summary
The invention relates to an operating state circuit for actuating an inverter (3), which supplies an n-phase electrical machine (5) with an n-phase supply voltage via phase connections (4a, 4b, 4c), wherein n = 1, comprising an evaluation device (6) which is connected to the phase connections (4a, 4b, 4c) of the inverter (3) and which is configured to detect output voltages of the inverter (3) to the phase connections (4a, 4b, 4c) and to determine a speed of the electrical machine (5) on the basis of the detected output voltages, and an actuating device (7) which is coupled to the evaluation device (6) and which is configured to switch to an idle state or an active short-circuit in dependence on the determined speed of the inverter (3).