Electric Machine Short-Circuit Control for Low Transient Current
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Solution Overview
Problem
Existing methods for transitioning an electric machine into a safe state during fault events, such as hard and soft AKS, can result in high transient short-circuit currents that demagnetize the rotor's permanent magnets or cause overloading, without optimizing the transition time and voltage levels.
Innovation Solution
A method that ascertains a desired trajectory for the motor current vector from the current working point to the short-circuit working point, using a model predictive controller to predict a pilot control action, ensuring the actual current vector follows this trajectory, thereby optimizing the transition time and minimizing transient currents and voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If hard AKS is performed to transition the electric machine into a safe state, then the machine reaches the safe state quickly, but high transient short-circuit currents arise that can demagnetize permanent magnets of the rotor
Solution Approach 1:
The patent applies preliminary action by predicting the pilot control action before the actual short-circuiting occurs. The model predictive controller calculates the optimal control sequence in advance, determining the desired trajectory for the current vector from the actual working point to the short-circuit working point. This pre-calculation allows the system to prepare the optimal path that minimizes harmful transient currents while ensuring quick transition to the safe state.
Solution Approach 2:
The patent implements dynamics by using a dynamic model of the electric machine that accounts for the actual operating point. The model predictive controller continuously adapts the control strategy based on the current state of the machine, allowing the transition path to be optimized in real-time according to the actual working conditions. This dynamic approach enables the system to adjust the transition trajectory to minimize transient currents while maintaining fast response.
2Object-generated harmful factors
If soft AKS is performed to reduce transient short-circuit current, then the harmful current is reduced, but the transition time to the safe state increases
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the control parameters along the desired trajectory. The model predictive controller modifies the voltage vectors applied to the motor winding according to the calculated optimal path, changing the electrical parameters in a controlled manner. This allows the system to reduce transient currents by following an optimized trajectory that passes through intermediate states, rather than making abrupt transitions.
Solution Approach 2:
The patent implements a form of skipping by using predictive control to calculate the entire optimal trajectory in advance. Instead of gradually transitioning through many intermediate steps, the controller determines the optimal path and executes it efficiently, skipping unnecessary intermediate calculations and directly applying the predicted control actions. This reduces the overall transition time while still maintaining low transient currents.
3Ease of manufacture
If the motor winding is short-circuited from the current actual working point (hard AKS), then the transition is simple and direct, but the transient short-circuit current becomes excessively high causing demagnetization
Solution Approach 1:
The patent introduces an intermediary element - the model predictive controller - that mediates between the simple hard AKS approach and the need to reduce transient currents. The controller acts as an intelligent intermediary that calculates the optimal transition path and applies appropriate voltage vectors during the short-circuiting process. This intermediary control layer adds computational complexity but eliminates the harmful transient currents by guiding the transition through an optimized trajectory.
Solution Approach 2:
The patent replaces the direct mechanical/electrical switching approach of hard AKS with a computational control system. Instead of simply closing switches to create a direct short-circuit, the system uses a model predictive controller that performs calculations and applies controlled voltage sequences. This substitution of computational control for direct electrical switching enables the system to achieve the same safety function while minimizing harmful transient effects.
Data Source
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 electrical energy store (4) by means of a 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 trajectory (T) for an actual current vector (iactual,dq) of an electric motor current flowing through the motor winding is ascertained, said desired trajectory (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 trajectory (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 (iactual,dq) at least substantially matches the desired trajectory (T).