Motor Control Timing to Avoid Zero-Cross Current Noise
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Solution Overview
Problem
Conventional motor control systems face challenges in achieving stable control due to noise interference at zero-cross points of motor current, leading to detection errors and inefficiencies, particularly at high rotational speeds, affecting motor efficiency and causing vibration and undesired sound in applications like vacuum cleaners and hand dryers.
Innovation Solution
A motor control device that includes a position detecting unit, an analog-digital converter, and a control circuit, where the AD converter is started and processed during specific periods excluding zero-cross points, with the prohibition period length decreasing as motor speed increases, to minimize noise influence and ensure stable control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If edge detection is used to detect rotor position from position sensor signal, then detection speed is improved, but noise from current polarity switching at zero-cross points causes detection errors
Solution Approach 1:
The patent extracts and removes the harmful zero-cross point periods from the signal processing timeline. By identifying and excluding the time periods when current polarity switches occur, the system prevents noise from contaminating the position sensor signal detection, thereby maintaining high detection speed without sacrificing accuracy.
Solution Approach 2:
The patent introduces an intermediary time period concept between the position sensor signal and the motor current. By defining a prohibited time period that excludes zero-cross points, the system creates a buffer zone that prevents direct interference between noisy current switching and position detection, allowing accurate edge detection without noise contamination.
2Speed
If analog-digital converter processes signals continuously, then control responsiveness is improved, but noise interference increases during zero-cross points
Solution Approach 1:
The patent applies periodic action by enabling the analog-digital converter only during permitted time periods and disabling it during prohibited zero-cross point periods. This periodic enable-disable operation allows the system to maintain high control responsiveness during clean signal periods while eliminating noise interference during current polarity switching events.
Solution Approach 2:
The patent implements preliminary anti-action by preemptively disabling the analog-digital converter before noise can contaminate the signal. By identifying prohibited time periods in advance and preventing converter operation during these periods, the system proactively blocks noise interference before it can affect the digital signal used for motor control.
3Productivity
If motor operates at high rotational speed, then productivity is improved, but noise influence and vibration increase
Solution Approach 1:
The patent applies dynamics by making the prohibited time period duration variable based on motor rotational speed. As rotational speed increases, the prohibited period is adjusted accordingly, allowing the system to maintain optimal noise filtering at all speeds. This dynamic adjustment enables high productivity at elevated speeds while continuously suppressing noise influence through adaptive timing control.
Data Source
AI summary
A motor control device includes a position sensor that detects a position of a motor, an AD converter that converts an analog signal, which is a detection value of a motor current, into a digital signal, and a control circuit that drives an inverter using an output signal of the AD converter. The control circuit starts the AD converter during a permission period, and performs processing for the analog-digital converter during an electrical half cycle including a permission period. The length of a prohibition period obtained by excluding a permission period from an electrical half cycle decreases as the rotating speed of the motor increases.