Rotor Current Estimation for Smooth Motor-to-Neutral Switching
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Solution Overview
Problem
Existing rotating electrical machines face challenges in smoothly transitioning from motor mode to neutral mode, leading to torque oscillations and overvoltages due to residual rotor current, which complicates the transition process and affects efficiency.
Innovation Solution
A control module estimates the rotor coil current using a specific formula, allowing for precise demagnetization and stator short-circuiting when the current is nearly zero, thereby reducing or eliminating torque oscillations and overvoltages, and accelerating the transition to neutral mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the stator is short-circuited to eliminate residual current quickly, then the transition speed to neutral mode is improved, but torque oscillations and overvoltages occur due to premature short-circuiting while rotor current is still present
Solution Approach 1:
The control module performs preliminary demagnetization of the rotor coil before short-circuiting the stator phases. By applying a reverse voltage to the rotor coil, the rotor current is reduced to zero in advance, ensuring that the subsequent stator short-circuit occurs only when the rotor is fully demagnetized, thus avoiding torque oscillations and overvoltages
Solution Approach 2:
The control module continuously monitors the rotor current and uses this feedback to determine the optimal timing for stator short-circuiting. The short-circuit command is issued only when the rotor current reaches zero, ensuring synchronized demagnetization and preventing harmful torque oscillations and overvoltages during the transition to neutral mode
2Object-generated harmful factors
If the demagnetization time is extended to ensure complete rotor current elimination, then torque oscillations are reduced, but the transition to neutral mode becomes slower
Solution Approach 1:
The control module applies reverse voltage to the rotor coil to actively demagnetize it before the stator short-circuit. This preliminary action rapidly reduces rotor current to zero, enabling the stator to be short-circuited immediately afterward without causing torque oscillations, thus achieving both fast transition and smooth operation
Solution Approach 2:
The control module changes the rotor coil voltage parameter by applying reverse voltage during demagnetization. This parameter change accelerates the reduction of rotor current, allowing the transition to neutral mode to complete faster while maintaining smooth torque characteristics without oscillations
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
This approach effectively minimizes torque surges and overvoltages, enhancing the efficiency of the transition from motor mode to neutral mode by accurately estimating and managing the rotor coil current, leading to a faster and more stable process.
Implementation Method 1
a value of resistance of the rotor coil... Irot[k-1] is the estimate of the rotor coil current previously calculated at time k-1 Vrot [k-1] is the previous rotor coil voltage at time k-1 Ts is the sampling time
Implementation Method 2
In rapid demagnetization, the rotor coil is powered in reverse from the motor mode, which demagnetizes more quickly
Implementation Method 3
a short circuit is made between the phases of the Stator, for example by closing the low stage MOSFETs of the inverter/rectifier, for a duration predetermined by example of around 10ms so that the residual current in the stator is eliminated in joule losses in the stator coils
Data Source
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AI summary
One aspect of the invention relates to a module for controlling a rotary electric machine for a motor vehicle, the control module comprising a calculating program, a value of the rotor coil voltage Vrot, a resistance value of the rotor coil Rrot, a value of the rotor coil induction Lrot and in that the programme estimates the rotor coil current Irot according to this formula: Irot[k] = Irot[k-1] + (Vrot[k-1] – Irot[k-1] x Rrot)/Lrot x Ts in which: • Irot[k-1] is the estimate of the rotor coil current previously calculated at time k-1, • Ts is the sampling time between the index k-1 and the index k, and in which, to switch from a motor mode to a neutral mode, said control module is configured to control a shorting of the phases of the stator after the estimated rotor coil current Irot is equal to a predetermined value.