Motor-Fan Unit PWM Synchronization for Stable Motor Control
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Solution Overview
Problem
The existing motor-driven fan assemblies for motor vehicles suffer from disrupted acquisition of characteristic quantities due to current peaks from MOSFET switches, leading to less responsive and stable control of the electric motor, with conventional low-pass filters not adequately addressing this issue and causing latency.
Innovation Solution
The acquisition of characteristic quantities is synchronized with respect to the rising and falling edges of the pulse-width modulated primary signal, allowing for a reduced cutoff frequency in the low-pass filter, thus avoiding disturbance from switchings and enabling error-free measurement, which can be achieved by triggering the acquisition at specific times relative to the pulse-width modulated secondary signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a low-pass filter is used to attenuate current spikes from MOSFET switching, then measurement stability is improved, but acquisition latency increases and response time deteriorates
Solution Approach 1:
The system performs preliminary action by triggering the acquisition exactly at the moment when the MOSFET switches are not switching (at the falling edge of the PWM signal). This timing ensures that the measurement is taken before any current spikes can occur, eliminating the need for heavy filtering while avoiding latency. The acquisition is proactively scheduled at the optimal moment in the PWM cycle.
2Measurement precision
If a low-pass filter with determined cutoff frequency is used to attenuate current spikes, then signal noise is reduced, but filter size and cost increase
Solution Approach 1:
The invention extracts the harmful current spikes from the measurement signal by carefully timing the acquisition to occur when the MOSFET switches are in a stable state (not switching). By taking the measurement at this specific moment in the PWM cycle, the noisy switching transients are excluded from the acquisition window, eliminating the need for complex filtering hardware.
3Loss of information
If acquisition is performed continuously without synchronization, then data coverage is improved, but acquisition is disrupted by current spikes from switchings
Solution Approach 1:
The system implements periodic action by synchronizing the acquisition to occur at regular, predictable intervals within each PWM cycle - specifically at the falling edge of the PWM signal. This periodic synchronization ensures that every acquisition happens at the same optimal moment in the switching cycle, consistently avoiding current spikes while maintaining continuous monitoring of the characteristic quantity.
Data Source
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AI summary
The present invention concerns a motor-fan unit (GMV) for a motor vehicle (V) comprising an electric motor (MOT) and an electronic control card (CD) for controlling said electric motor (MOT), said electronic control card (CD) comprising: - an acquisition device (ADC) for acquiring at least one characteristic variable (G) of said motor-fan unit (GMV); - an operating device (MC) configured to operate said electric motor (MOT) by means of a primary pulse width modulation signal (PWM1); characterised in that said operating device (MC) is further configured to send, to said acquisition device (ADC), a triggering signal (S) for triggering said acquisition, said triggering signal (S) being offset and synchronous with respect to said primary pulse width modulation signal (PWM1).