Hysteresis-based actuation of a vehicle drive with an alternating freewheeling and short-circuit state in the event of a fault
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Solution Overview
Problem
Existing electric vehicle drives face the risk of component damage due to high voltages or currents generated during generator mode when phase connections of the electric machine are open or actively short-circuited, particularly when a fault occurs, which can lead to demagnetization of permanent magnets and damage to inverter components.
Innovation Solution
Implement a hysteresis-based control method that alternates between a freewheeling state and an active short circuit (AKS) based on current and voltage limits to prevent sustained overcurrent or overvoltage, using a control device to adjust parameters and switch states to manage kinetic energy reduction safely.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the phase connections of the electric machine are open during coasting in generator mode, then the electric machine can generate electrical power, but a high voltage may occur which may destroy electrical components such as inverter components or intermediate-circuit components
Solution Approach 1:
The patent introduces an intermediary control mechanism (the inverter's switching devices) that mediates between the electric machine's generator mode and the electrical components. By controlling the switching states of the inverter bridges, the system can redirect or limit the generated electrical energy, preventing excessive voltage from reaching vulnerable components while still allowing power generation to occur.
Solution Approach 2:
The patent dynamically changes the electrical parameters (voltage, current, switching states) of the inverter system based on the operating conditions. By adjusting the switching frequency and state of the inverter bridges, the system can control the voltage level generated during coasting, transforming the harmful high voltage condition into a controlled parameter that protects components while maintaining energy generation.
2Object-affected harmful factors
If the electric machine is operated in an active short circuit during coasting in generator mode, then the phase connections are connected to one another, but a current may arise which may likewise be damaging for electrical components of the drive, in particular for the switches of the inverter
Solution Approach 1:
The patent employs periodic switching action of the inverter bridges to control the current flow during active short circuit operation. By alternately switching the bridges on and off at controlled intervals, the system can limit the average current while still maintaining the short circuit connection, preventing sustained overcurrent that would damage the inverter switches.
Solution Approach 2:
The patent introduces dynamic control of the inverter switching states based on real-time current and voltage measurements. The switching frequency and duty cycle are dynamically adjusted to maintain current within safe limits while preserving the active short circuit function, transforming a static potentially harmful condition into a dynamically controlled safe operation.
3Speed
If a fault occurs and the vehicle is coasting in generator mode, then kinetic energy needs to be reduced, but sustained overcurrent may lead to demagnetization of permanent magnets and sustained overvoltage may cause long-lasting damage to components
Solution Approach 1:
The patent implements a feedback control mechanism that continuously monitors current and voltage levels during fault conditions and adjusts the inverter switching states accordingly. When current or voltage approaches dangerous thresholds, the controller modifies the switching pattern to reduce the generated power, thereby protecting components while still achieving vehicle deceleration through controlled energy dissipation.
Solution Approach 2:
The patent prepares protective measures in advance by pre-configuring the inverter switching patterns to limit current and voltage excursions before they reach damaging levels. The control system anticipates potential harmful conditions and applies protective switching sequences that cushion against overcurrent and overvoltage, preventing demagnetization and component damage before they can occur.
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 method effectively limits current and voltage fluctuations, preventing component damage and ensuring safe operation by alternating between states to manage energy reduction without causing jerking or prolonged component stress.
Implementation Method 1
If a fault occurs while driving, electrical power is generated in generator mode of the electric machine while the vehicle is coasting
Implementation Method 2
What is proposed, in accordance with a hysteresis response with regard to a phase current generated by the generator mode of the electric machine, and in accordance with a hysteresis response with regard to a DC voltage generated by the generator mode of the electric machine, is to alternately execute a freewheel and an active short circuit
Data Source
AI summary
A method for actuating a vehicle drive. If a fault occurs in the electric drive or in a component connected thereto, the inverter generates an AKS state in the form of an active short circuit of phase connections of the electric machine, or a freewheeling state of the electric machine. Once the fault has occurred, steps AKS and F are executed alternately. Step AKS: setting the AKS state if a phase current flowing through the phase connections is below a first current limit and changing over to step F if the phase current reaches the first current limit; Step F: setting the freewheeling state if a DC voltage generated by the electric machine is below a first voltage limit and changing over to step AKS if the DC voltage is above the first voltage limit. A changeover from step AKS to step F if the phase current reaches a second current limit below the first current limit. A changeover from step F to step AKS if the DC voltage reaches a second voltage limit below the first voltage limit. A vehicle drive and a corresponding control program are used to execute the method.