Motor Control Device Leakage Current Detection
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Solution Overview
Problem
In motor control devices, the complex circuit structure of motor current detectors leads to time delays when converting currents to analog voltages, resulting in timing mismatches and increased false detection of leakage currents during power conversion element switching.
Innovation Solution
A motor control device with a stop signal controller that delays the stop signal by the time it takes for the motor current detector to convert the leakage current to an analog signal, allowing the ΔΣ AD conversion block to stop operating only when necessary, thereby reducing false detection of leakage currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the motor current detector uses a complex circuit structure to detect high current (several hundred amperes), then the detection capability is improved, but a time delay occurs when converting current to analog voltage
Solution Approach 1:
The stop signal controller generates the stop signal in advance before the leakage current occurs. By predicting when the leakage current will happen based on the PWM switching timing, the system prepares the stop signal beforehand, ensuring that the ΔΣ AD conversion block stops operating at the correct time without waiting for the delayed current conversion to complete.
2Reliability
If the ΔΣ AD conversion block stops operating while leakage current is occurring, then false detection is reduced, but a timing mismatch occurs due to conversion delay
Solution Approach 1:
The stop signal controller uses feedback from the PWM switching signal timing to determine when to generate the stop signal. By monitoring the PWM switching timing and calculating when leakage current will occur, the controller adjusts the stop signal timing accordingly, creating a closed-loop system that compensates for the conversion delay and prevents false detection.
3Ease of operation
If the stop signal is generated without considering conversion delay, then the control is simple, but timing mismatch causes false detection of leakage current
Solution Approach 1:
The stop signal controller acts as an intermediary between the PWM switching signal and the ΔΣ AD conversion block. It receives the PWM switching signal, calculates the appropriate stop timing by accounting for conversion delay, generates the stop signal with correct timing, and sends it to the ΔΣ AD conversion block. This intermediary function maintains control simplicity while ensuring accurate timing.
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 configuration effectively reduces false detection of leakage currents caused by power conversion element switching, even with delays in current conversion, improving the accuracy of motor current detection and reducing unnecessary torque and microvibration.
Implementation Method 1
Motor current detector 11 converts a current that flows in a winding in response to the drive voltage to an analog voltage
Implementation Method 2
ΔΣ AD conversion block 15 converts the analog voltage to a digital signal
Implementation Method 3
Power converter 18 applies a drive voltage to a winding by switching a switching element (power conversion element) on or off in accordance with the PWM switching signal
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A motor control device (10) that detects a motor current through ΔΣ AD conversion includes a stop signal generator (19) and a stop signal controller (20). When a difference between a maximum value and a minimum value of three phase voltage command values to be applied to a motor (30) is smaller than or equal to a predetermined threshold, a stop signal that causes the ΔΣ AD conversion to stop is output with a delay by the time corresponding to a delay in current detection while a leakage current caused by on and off of a power conversion element is occurring.