Electric Machine Fault Switching for DC Bus Overvoltage Control
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Solution Overview
Problem
Existing fault handling methods in electric machines of motor vehicles, particularly in high-voltage DC networks, lead to rapid voltage increases and potential damage to semiconductor components due to freewheeling conditions, and active short circuit conditions result in high currents, necessitating overdimensioned intermediate circuits or thermal disruptions.
Innovation Solution
A two-stage fault response method where a primary fault signal initiates a freewheeling condition for the electric machine's windings, followed by an active short circuit condition if a secondary fault signal indicates battery nonreceptiveness, using an intermediate circuit energy accumulator designed for normal operation, thus preventing further power input and reducing ASC currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a freewheeling condition is produced for the electric machine windings upon primary fault signal, then the electric machine is protected from fault damage, but rapid voltage increase occurs in the DC voltage network potentially damaging semiconductor components
Solution Approach 1:
The patent introduces an intermediate energy accumulator (capacitor) in the DC voltage network as a mediator to absorb the voltage surge caused by freewheeling. This intermediary component prevents the harmful voltage increase from reaching the semiconductor components, thus resolving the contradiction between fault protection and voltage damage prevention.
Solution Approach 2:
The energy accumulator is pre-configured in the DC voltage network to provide cushioning against voltage surges before they occur. When a freewheeling condition is activated, the accumulator immediately absorbs the excess energy, preventing rapid voltage increase and protecting semiconductor components without requiring active response from the control system.
2Object-affected harmful factors
If an active short circuit condition is produced to prevent further power input into the DC voltage network, then voltage increase is prevented, but high currents occur causing thermal disruption or requiring overdimensioned intermediate circuits
Solution Approach 1:
Instead of immediately applying full active short circuit action which causes high currents, the patent uses a partial action approach by relying on the pre-configured energy accumulator to handle the voltage surge. The accumulator absorbs the excess energy partially, allowing the system to prevent voltage increase without requiring the excessive current of a full active short circuit, thus avoiding thermal disruption.
3Object-affected harmful factors
If the intermediate circuit is overdimensioned to handle fault conditions, then semiconductor components are protected from voltage damage, but device complexity and cost increase
Solution Approach 1:
The energy accumulator is pre-configured with sufficient capacity to handle fault conditions before they occur. This beforehand cushioning allows the intermediate circuit to be designed for normal operation parameters rather than being overdimensioned for fault conditions, reducing device complexity and cost while still protecting semiconductor components during faults.
Data Source
AI summary
A method for operating an electric machine including a rotor and a stator is connected to a first or a second power electronics assembly (PEA), the first or the second PEA including a circuit arrangement that produces a freewheeling condition or an active short circuit condition for a winding of the rotor or the stator, to a DC voltage network having a battery, and the first or the second PEA including an inverter formed by the circuit arrangement. The method includes, in response to a primary fault signal indicating a fault the first or the second PEA, actuating the first or the second PEA to produce the freewheeling condition, and in response to a secondary fault signal indicating a nonreceptiveness of the battery for power fed by the electric machine to the DC voltage network, actuating both the first and the second PEA to produce the active short circuit condition.