Motor Control Device Clock Stop Signal for Leakage Current
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Solution Overview
Problem
In motor control systems using PWM control, the ΔΣ AD converter is affected by leak current, leading to inaccurate detection of motor current and resulting in undesired torque and minute vibrations, especially during servo-lock and low-speed rotation.
Innovation Solution
A motor control device and method that includes a stop signal generator to stop the AD conversion clock for a predetermined period based on the timing of PWM switching, reducing the impact of leak current on detection accuracy by temporarily halting the operation of the ΔΣ AD converter and AD conversion decimating filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the ΔΣ AD converter continuously operates to detect motor current, then the detection responsiveness is improved, but the detection accuracy deteriorates due to leak current during PWM switching
Solution Approach 1:
The AD converter operates periodically rather than continuously. A stop signal is generated based on PWM switching timing to halt the AD converter during periods when leak current would corrupt measurements. This periodic operation allows continuous monitoring capability while avoiding contamination from switching transients, thus resolving the contradiction between responsiveness and accuracy.
2Duration of action of stationary object
If the AD converter operates during PWM switching, then continuous monitoring is maintained, but unwanted current components are introduced into the detection signal
Solution Approach 1:
The harmful leak current components are extracted or removed from the detection system by stopping the AD converter during PWM switching events. The stop signal generator identifies switching timing and temporarily halts conversion operations, effectively separating the useful continuous monitoring function from the harmful switching interference periods.
3Measurement precision
If the AD converter runs without interruption, then detection coverage is maximized, but motor vibration increases due to undesired torque from inaccurate current detection
Solution Approach 1:
The PWM switching timing, which initially causes harmful leak current, is converted into a useful trigger signal. The stop signal generator uses the PWM switching events to precisely control when the AD converter should be halted, transforming the switching phenomenon from a source of error into a synchronized control mechanism that prevents measurement corruption while maintaining overall detection coverage.
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 reduces the deterioration in detection accuracy caused by leak current, thereby minimizing undesired torque and suppressing minute vibrations in the motor.
Implementation Method 1
ΔΣ (delta sigma) AD converter 92, as shown in Fig. 8, in AD conversion unit 95 has been proposed
Implementation Method 2
In a general PWM (Pulse Width Modulation) control system for controlling motor torque
Implementation Method 3
voltage at both ends of the shunt resistance changes by this leak current
Data Source
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Figure 3
AI summary
A motor control device has a motor current detector for detecting current in windings to control the operation of a motor with a stator having three-phase windings. The motor control device includes a digital controller for outputting a PWM switching signal, a power converter for applying drive voltage to the windings using the PWM switching signal, a motor current detector for converting current flowing in the windings to analog voltage, a ΔΣ AD converter for converting the analog voltage to a 1-bit digital signal, an AD conversion decimating filter for generating a detected motor current value from the 1-bit digital signal, a clock generator for generating a clock for the ΔΣ AD converter and the AD conversion decimating filter, and a stop signal generator for generating a clock stop signal for stopping the clock of the clock generator for a predetermined period. The stop signal generator generates the clock stop signal with a predetermined pulse width based on a timing of the PWM switching signal, and the clock generator stops the clock for a period of the predetermined pulse width, using the clock stop signal.