Electric Machine Short-Circuit Control With Current Vector Trajectory
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Solution Overview
Problem
Existing methods for short-circuiting the motor winding of an electrical machine during faults can result in high transient short-circuit currents, potentially demagnetizing the rotor's permanent magnets and causing overloading.
Innovation Solution
A method that determines a target trajectory for the actual current vector from the current operating point to a short-circuit operating point, using feedforward control to control the power electronics and achieve a time-optimized and low-transient short-circuit current transition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If hard short-circuiting is used to transfer the machine to a safe state, then the short-circuiting is achieved quickly, but high transient short-circuit currents occur that can demagnetize permanent magnets
Solution Approach 1:
The patent applies preliminary action by determining a target trajectory for the current vector before executing the short-circuiting operation. The feedforward control is calculated in advance based on the target trajectory, which runs from the current operating point to the short-circuit operating point. This allows the power electronics to be controlled smoothly along the predetermined path, avoiding sudden current spikes while maintaining relatively fast transition speed.
Solution Approach 2:
The patent implements dynamics by using a dynamic feedforward control approach that adapts the short-circuiting process to the current operating conditions. The target trajectory and corresponding feedforward control are determined based on the actual current operating point, allowing the system to optimize the transition path dynamically. This enables smooth current reduction while maintaining efficient fault response.
2Object-generated harmful factors
If soft short-circuiting is used to reduce transient short-circuit current, then demagnetization is prevented, but the transition time increases
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the voltage vector sequence based on the current operating point and target trajectory. The feedforward control calculates optimal voltage vectors that guide the current along the predetermined path to the short-circuit operating point. This allows the system to maintain low transient currents while minimizing transition time through optimized parameter selection at each step.
Solution Approach 2:
The patent implements feedback by continuously monitoring the actual current operating point and using it to determine the target trajectory and feedforward control. The control system adjusts the voltage vectors based on the current state, ensuring the system follows the optimal path to the short-circuit operating point. This closed-loop approach balances transition speed with transient current limitation.
3Object-generated harmful factors
If the power electronics are controlled to achieve precise current vector trajectory, then transient currents are minimized, but control complexity increases
Solution Approach 1:
The patent reduces control complexity by determining the target trajectory and calculating the feedforward control in advance, before the short-circuiting operation begins. The target trajectory is pre-calculated based on the current operating point and the desired short-circuit operating point. This preliminary calculation simplifies the real-time control task, as the system only needs to follow the predetermined path using the pre-computed feedforward control signals.
Data Source
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AI summary
The invention relates to a method for operating an electric machine (2) comprising a rotatably mounted rotor and a motor winding that is electrically connected to an electric energy store (4) by means of power electronics (3). In said method, the machine (2) and/or an apparatus comprising the machine (2) is/are monitored in respect of fault events, and the motor winding is short-circuited by triggering the power electronics (3) upon detection of a fault event. According to the invention, a desired path (T) for an actual current vector (iIst, dq) of an electric motor current flowing through the motor winding is ascertained, said desired path (T) extending from a current actual working point (AP1) of the machine (2) to a short-circuit working point (AP2) of the machine (2), a pilot control action is predicted according to the desired path (T), and the power electronics (3) are triggered to short-circuit the motor winding according to the pilot control action in such a way that when the motor winding is short-circuited, a curve (V) of the actual current vector (iIst, dq) at least substantially matches the desired path (T).