Permanent Magnet Motor Braking Torque Control During Power Loss
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Solution Overview
Problem
Conventional speed control and braking torque systems for permanent magnet electrical machines are dependent on an external power supply, which becomes problematic when the supply fails, particularly in situations like electrically operated clutch actuator systems where abrupt clutch closure can occur.
Innovation Solution
A device with a switching element that short-circuits the electric machine based on the induced voltage, allowing for speed-dependent braking torque control without an external energy supply, utilizing a blocking element for rectification, a delay element for voltage smoothing, and threshold-controlled hysteresis to manage braking torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional speed control and braking torque systems are used, then the system operates normally under power supply, but the system fails to control speed when power supply fails
Solution Approach 1:
The electric machine generates its own induced voltage through rotation, which is used to control the switching element and regulate braking torque. This self-powered control mechanism eliminates dependency on external power supply for braking control, allowing the system to maintain reliability during power failures.
Solution Approach 2:
The control system uses the induced voltage generated by the rotating electric machine as feedback to regulate the switching element. This feedback mechanism enables speed-dependent braking torque control, where the braking force automatically adjusts based on the machine's rotational speed without requiring external power or complex sensors.
2Force
If the switching element continuously short-circuits the electric machine, then strong braking torque is generated, but the braking torque cannot be modulated for speed control
Solution Approach 1:
The switching element operates in periodic on-off cycles, switching between conducting and non-conducting states based on the induced voltage threshold. This periodic action creates pulse-width modulated braking torque, allowing smooth speed control through duty cycle adjustment rather than continuous full-strength braking.
Solution Approach 2:
The braking torque is dynamically adjusted based on the rotational speed of the electric machine. As speed changes, the induced voltage changes, automatically modulating the switching element's operation to provide appropriate braking force for speed control without requiring external control signals.
3Extent of automation
If the induced voltage is used directly to control the switching element, then speed-dependent control is achieved, but voltage spikes may damage components
Solution Approach 1:
A clamping diode is connected in parallel with the switching element to provide a safe discharge path for induced voltage spikes before they can damage components. This protective measure is built into the circuit design to cushion against voltage surges that occur during switching operations or sudden speed changes.
Solution Approach 2:
A delay element is introduced between the induced voltage source and the switching element control circuit. This intermediary component smooths and conditions the voltage signal, filtering out harmful spikes while preserving the speed-dependent control functionality, thus protecting the switching element from voltage damage.
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
Ensures controllable braking torque even during power supply failures, maintaining the electric machine's speed within a desired range or reducing it to a standstill, preventing abrupt movements like clutch closure.
Implementation Method 1
The switching element is controlled as a function of the induced voltage generated in the electric motor itself. This induced voltage is caused by the rotating field of the permanent magnets in the windings of the electric motor and is therefore dependent on the rotational speed of the rotor.
Implementation Method 2
A blocking element, which takes over the function of a rectifier, is used to rectify the induced voltage generated in the electric machine.
Implementation Method 3
a delay element is provided, which serves to selectively transmit an input voltage Ue in such a way that the output voltage Ua of the delay element can be better used as a control voltage for a switching element
Data Source
Figure 1
Figure 2
AI summary
The invention relates to a device for speed-dependent braking torque control for electrical machines excited by permanent magnets, wherein a switching element (2) deliberately short-circuits the electrical machine (3) and thus generates a braking torque on the rotor of the electrical machine (3) when the power supply (6) is interrupted and there is at the same time an increase in the speed n caused externally depending on the induced voltage of the electrical machine (3). If the induced voltage falls below a defined value, the switching element (2) reverses the short-circuited state of the electrical machine (3), as a result of which the braking torque reduces to zero and the speed n increases again. The speed n can thus be controlled within a window by alternately opening and closing the switching element (2).