AC Motor Braking via Active Current Feedback
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Solution Overview
Problem
Existing braking methods for alternating current electric motors, particularly asynchronous motors, face limitations due to inaccurate or delayed feedback from DC-Link voltage detection, which is inadequate for rapid changes in motor operation, leading to inefficiencies and increased costs and dimensions in energy dissipation circuits.
Innovation Solution
A method that uses active current feedback signals from the motor's stator windings to adjust magnetization current, increasing copper and iron losses to compensate for braking energy, while maintaining a constant deceleration ramp, by generating an activation signal based on current error and integrating it with control signals to manage power dissipation effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If DC-Link voltage detection is used for braking control, then the control system can detect braking energy accumulation, but the feedback is inaccurate and delayed due to capacitor charging times, making it inadequate for rapid motor operation changes
Solution Approach 1:
The patent implements a feedback mechanism using active current detection from the motor's stator windings. The controller continuously monitors the active current component and generates feedback signals to adjust the magnetization current, enabling real-time response to rapid motor operation changes during braking. This replaces the delayed DC-Link voltage detection with immediate current-based feedback.
Solution Approach 2:
The patent substitutes the voltage-based detection system with a current-based detection system. By detecting the active current component directly from the stator windings, the system replaces the indirect and delayed voltage measurement approach with a direct and immediate current measurement, eliminating the feedback delay caused by capacitor charging times.
2Loss of energy
If an energy dissipation circuit with additional resistor is used, then braking energy can be dissipated effectively, but the costs and dimensions of the dissipation circuit increase significantly for powers higher than 200kW
Solution Approach 1:
The patent enables the motor itself to serve as the energy dissipation device by increasing its magnetization during braking. The controller increases the magnetization current beyond normal levels, causing the motor to dissipate braking energy through increased copper and iron losses within its own structure. This eliminates the need for external energy dissipation circuits with additional resistors, reducing both cost and dimensionality.
Solution Approach 2:
The patent makes the motor perform multiple functions: it acts as both the drive motor during normal operation and as the energy dissipation device during braking. By controlling the magnetization current dynamically, the motor can switch between motor mode and generator/braking mode, eliminating the need for separate dedicated braking components.
3Stability of the object's composition
If magnetization is increased during braking to compensate for generated energy, then the deceleration ramp can be maintained unchanged, but additional dissipation circuits are required to handle the increased energy
Solution Approach 1:
The patent enables the motor to dissipate the increased energy generated by elevated magnetization through its own internal losses. By operating the motor in a controlled generator mode during braking, the increased magnetic flux generates higher copper and iron losses that directly dissipate the braking energy, maintaining stable deceleration without requiring external dissipation circuits.
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 provides faster and more accurate feedback, allowing for efficient energy dissipation without additional dissipation circuits, reducing costs and dimensions of energy dissipation components, and maintaining consistent braking performance across varying motor states.
Implementation Method 1
In particular conditions, the electric motor is configured to operate as generator, by transforming the mechanical energy into electric energy
Implementation Method 2
which provide a step of increasing the magnetization of the motor following the generation of a torque disagreeing with the sense of rotation by the motor itself, i.e. at the beginning of a step of decelerating or braking of the motor in order to increase the losses by Joule effect in the motor itself
Implementation Method 3
The iron losses are the losses due to eddy currents and rotor and stator magnetic core hysteresis
Implementation Method 4
The iron losses are the losses due to eddy currents and rotor and stator magnetic core hysteresis
Data Source
Figure 1
Figure 2
Figure 3~6
AI summary
The invention relates to a method for braking an alternating current (AC) electric motor (M). The motor can be actuated by means of an electronic control apparatus (100; 200) which comprises: - a frequency converter stage (10; 10'), adapted to generate a plurality of Pulse Width Modulation PWM digital signals (11) on the basis of a first (V; Isdref) and a second (θ; Isqref) control signal; - a power stage (20), adapted to transfer electric power (Pel) to the motor (M) to actuate it on the basis of such digital signals (11). The first control signal (V; Isdref) is configured to control a magnetization current supplied to the motor (M). The method comprises the steps of: - detecting first current signals (Ia, Ib, Ic) indicative of actual currents absorbed by the motor (M); - generating a feedback signal (Iac) indicative of an active current of the motor (M) starting from such first current signals (Ia, Ib, Ic); - comparing the current feedback signal (Iac) with a current threshold (Iaref) to generate a current error signal (E). For levels of feedback signal (Iac) lower than the current threshold (Iaref), the method comprises the further steps of: - generating an activation signal (ΔV; ΔI) starting from the current error signal (E); - summing the activation signal (ΔV; ΔI) to the first control signal (V; Isdref) to increase the magnetization current (Im) to increase an electric power dissipation in the motor. For levels of feedback signal (Iac) higher than said current threshold (Iaref), inhibiting the generation of the activation signal (ΔV; ΔI).