AC Motor Rotation Detection via Freewheeling Current Analysis
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Solution Overview
Problem
Conventional methods for detecting the rotation direction of an AC motor during re-start after an instantaneous electric power interruption are inaccurate, especially for synchronous motors with large inertial loads, leading to unstable control and potential excessive current flow, particularly in applications like air conditioning and water supply systems.
Innovation Solution
The method involves using a shunt resistor within the electric power conversion device to detect the amplitude of the supply current and determine the rotation direction by analyzing the inductive voltages and freewheeling current patterns at specific timing points, allowing for quick and accurate detection of the motor's rotation direction during re-start.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional pulse converter circuits are used to detect rotation direction, then rotation direction can be detected, but the circuit complexity increases and detection accuracy during re-start is insufficient
Solution Approach 1:
The patent extracts the rotation direction detection function from complex pulse converter circuits and implements it using simple voltage comparison between two phases. By taking out only the essential detection function and implementing it through basic voltage comparison, the patent achieves accurate rotation direction detection during re-start without requiring complex pulse converter circuits, thus resolving the contradiction between measurement precision and device complexity
Solution Approach 2:
The patent introduces an intermediary approach by using voltage comparison as a mediator between the motor's electrical state and rotation direction detection. Instead of directly using complex pulse converters, the patent uses voltage comparison as an intermediary mechanism that simplifies the detection process while maintaining accuracy, especially during re-start conditions
2Reliability
If re-start is performed without accurate rotation direction detection, then the system can restart quickly, but control stability deteriorates and excessive current may flow
Solution Approach 1:
The patent applies preliminary action by detecting the rotation direction before the re-start operation begins. By using voltage comparison to determine rotation direction in advance, the system prepares the control parameters beforehand, ensuring stable control when re-start occurs without causing excessive current flow or control instability, thus resolving the contradiction between reliability and loss of time
Solution Approach 2:
The patent uses feedback by continuously monitoring the voltage relationship between phases and using this information to determine rotation direction. This feedback mechanism ensures that the control system has accurate information about the motor's state before re-start, enabling stable control and preventing excessive current flow while maintaining quick re-start capability
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 enables precise detection of the AC motor's rotation direction, preventing unstable control and excessive current flow, ensuring reliable re-starting even during abnormal power conditions, and simplifies the circuitry by reducing the need for multiple pulse converters.
Implementation Method 1
using a shunt resistor within the electric power conversion device to detect the amplitude of the supply current
Implementation Method 2
analyzing the inductive voltages and freewheeling current patterns at specific timing points
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
In a method for detecting rotation direction of an AC motor, quickly and correctly, when re-starting the AC motor after generation of an instantaneous electric power interruption, and also an electric power conversion device for the AC motor mentioned above, there are provided a converter 21, a smoothing capacitor 22, an inverter 23 for inverting a DC electric power from the converter into a three (3) phase AC power having a desired frequency thereof, and a controller/driver portion 4 for driving/controlling switching elements building up that inverter, wherein detection is made at a timing "tA" or "tB" when AC voltages of U-phase and V-phase among three (3) phases of AC inductive electric powers from the AC motor intersect with each other, and when supplying the three (3) phase electric power to the AC motor, again, after stoppage of an output of that electric power conversion device, a flow path for freewheeling current is formed between the inverter and the AC motor by driving part of the switching elements building up the inverter at the timing detected, and the rotation direction of the motor is determined depending on the freewheeling current detected.