Stepper Motor Driver PWM Control to Prevent Current Overshoot
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Driver devices for stepping motors face challenges in preventing current overshoot during PWM constant-current control, particularly in applications like hypochlorous acid water generation, where the impedance of the coil and water quality resistance can lead to excessive current magnitude.
Innovation Solution
The driver device employs an H-bridge circuit controlled by a control circuit and a pulse generation circuit, which adjusts the supply and decay modes to prevent current overshoot by skipping the switch to the supply mode when the set current value is reached, allowing the decay mode to continue and adjusting the number of skips based on the output current's proximity to the set value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PWM constant-current control is used to maintain output current at target value, then current control precision is improved, but current overshoot occurs during mode switching
Solution Approach 1:
The control circuit performs preliminary detection of current magnitude before mode switching occurs. When the output current is detected to be equal to or greater than a predetermined threshold before switching from decay mode to supply mode, the control circuit preemptively prevents the switch transition, thereby avoiding current overshoot before it can occur.
Solution Approach 2:
The control circuit continuously monitors the output current magnitude and uses this feedback information to make real-time decisions about mode switching. The feedback mechanism compares the detected current against a threshold value and adjusts the switching behavior accordingly, preventing overshoot while maintaining precise current control.
2Speed
If switch to supply mode is performed frequently to maintain current, then current response speed is improved, but switching losses increase
Solution Approach 1:
The control circuit allows the output current to temporarily exceed the target current value by skipping the decay mode transition, rather than performing frequent partial switching operations. This partial action approach reduces the total number of switch transitions while still maintaining acceptable current control, thereby reducing switching losses.
Solution Approach 2:
The control circuit uses periodic detection of output current magnitude at specific intervals (before mode switching) to determine whether to proceed with switching. This periodic checking mechanism optimizes the timing of switching operations, reducing unnecessary transitions and associated energy losses while maintaining current response performance.
3Productivity
If decay mode is used to reduce current magnitude, then current reduction efficiency is improved, but current may drop below target value
Solution Approach 1:
The control circuit performs preliminary detection of current magnitude before initiating decay mode. By checking whether the current exceeds the threshold before switching, the control circuit ensures that decay mode is only activated when appropriate, preventing unnecessary current reduction that would cause the current to drop below the target value.
Solution Approach 2:
The control circuit uses real-time feedback on current magnitude to regulate the use of decay mode. The feedback mechanism ensures that decay mode is activated only when the current is sufficiently above the target, maintaining current accuracy while still achieving efficient current reduction when needed.
Data Source
AI summary
A driver device (1) includes a pulse generation circuit (5) that generates, within one period, a pulse waveform (Spl) with a first voltage level in a first period (T1) and a pulse waveform with a second voltage level in a second period (T2). A control circuit (2) makes the first period equal to a minimum on period (Tminon) to perform a supply mode for the minimum on period and, if at the end of the minimum on period the output current (Iout) has reached the set current value (Iset), the control circuit makes a switch to a decay mode and performs a skip of a switch to the supply mode at the end of the second period.