Motor Driving Device PWM Current Sampling Timing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing motor driving circuits face challenges in accurately detecting phase current direction due to switching noise and short PWM signal durations, leading to incorrect current detection and unstable motor control.
Innovation Solution
A motor driving device with a detection unit and control unit that samples current only during predetermined PWM signal durations, using a detection resistor and A/D converter to generate a PWM signal for feedback control, and adjusts sampling based on error current signal thresholds to ensure accurate phase current detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If current detection is performed at point C using an inexpensive part, then cost is reduced, but current direction cannot be determined due to bidirectional current flow
Solution Approach 1:
The control unit determines the current detection timing in advance based on PWM signal timing before actual current detection occurs. By pre-determining when to sample current during specific PWM phases (when only one switch is ON), the system ensures accurate direction detection while using simple detection circuitry at point C.
2Ease of operation
If PWM signal switching between high and low is performed, then motor control is achieved, but switching noise is generated that overlaps with detected current values
Solution Approach 1:
The invention extracts and isolates the current detection operation from the PWM switching noise by performing detection only during specific phases when switching noise is minimal. The control unit identifies timing windows where current detection can be performed separately from the noisy switching events, effectively separating the detection function from the switching function.
Solution Approach 2:
The control unit pre-determines the PWM signal state and selects appropriate current detection timings before actual detection occurs. By planning detection timing in advance based on expected PWM states, the system avoids detecting current during high-noise switching transitions while maintaining effective motor control.
3Speed
If current detection is performed during very short time periods when PWM signal is low, then control responsiveness is improved, but detection accuracy deteriorates due to insufficient discharge time of gate charges
Solution Approach 1:
The control unit pre-determines whether the PWM low-level period is sufficiently long before initiating current detection. By evaluating the PWM signal characteristics in advance and selecting detection timing accordingly, the system ensures that detection only occurs when switching has completed and gate charges are fully discharged, guaranteeing accurate detection while maintaining responsiveness.
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 allows for precise detection of motor current direction and stable motor control, reducing errors and noise, even during short PWM signal periods.
Implementation Method 1
a detection resistor and A/D converter to generate a PWM signal
Implementation Method 2
an induced electromotive voltage is generated in the coil L1 in a direction in which it prevents a change in the electric current
Data Source
AI summary
A motor driving device includes a control unit configured to control a motor by obtaining a driving current of the motor, and generating a PWM signal for turning on/off a plurality of switching elements based on a difference between the driving current and a target value. If a time period in which the PWM signal is at the high level is longer than a predetermined time period, the control unit performs sampling of an electric current during the time period in which the PWM signal is at the high level, whereas if the time period in which the PWM signal is at the high level is shorter than or equal to the predetermined time period, the control unit does not perform the sampling of the electric current during the time period in which the PWM signal is at the high level.