Brushless Motor Control Device Zero Crossing Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High-speed brushless motors in vehicle water pumps face challenges in accurately detecting rotor rotation position due to return current effects, leading to misdetection and prolonged time lags in rotation control normalization.
Innovation Solution
A brushless motor control device that determines the current-on phase based on successive zero crossings detected after a predetermined masking period, allowing the motor to restart current-on and normalize rotation control, even when current has been interrupted to all phases, thereby minimizing the effect of return current and ensuring accurate rotor position detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If zero crossing detection is performed using induction voltages in the current-off phase, then rotor rotation position can be detected, but misdetection occurs due to return current effects at high rotation speeds
Solution Approach 1:
The control device determines the current-on phase based on zero crossings detected after a predetermined masking period has elapsed since current-on interruption. This preliminary timing action avoids detecting zero crossings during the return current period, thereby preventing misdetection while maintaining accurate rotor position detection capability
Solution Approach 2:
The system dynamically adjusts the timing of zero crossing detection based on the masking period elapsed since current-on interruption. By making the detection timing variable and conditional rather than fixed, the system adapts to high-speed operation conditions where return current duration changes, thus maintaining detection reliability across different rotation speeds
2Reliability
If the inverter is reset and re-actuated upon detecting rotation position abnormality, then system safety is maintained, but rotation control normalization time is prolonged
Solution Approach 1:
The control device performs preliminary determination of the current-on phase based on zero crossings detected after the masking period, before full system reset is needed. This allows the system to normalize rotation control more quickly by re-establishing proper phase control without requiring a complete inverter reset, thus reducing normalization time while maintaining safety
Solution Approach 2:
Instead of completely resetting the inverter system upon detecting an abnormality, the control device recovers by determining the current-on phase based on valid zero crossings that occur after the masking period. This selective recovery approach discards only the problematic detection period while recovering control functionality, thereby minimizing time loss
3Measurement precision
If the return current masking period is set longer than the return current period, then zero crossing misdetection is avoided, but detection timing flexibility is reduced
Solution Approach 1:
The system uses a dynamic timing approach where the control device determines the current-on phase based on zero crossings detected after a predetermined masking period has elapsed. This dynamic timing adaptation allows the system to maintain accurate detection by avoiding the return current period while adapting to varying return current durations at different rotation speeds, thus preserving both precision and adaptability
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 solution promptly normalizes rotation control of the motor by eliminating the impact of return current and ensuring accurate detection of rotor position, reducing the time lag in rotation control and maintaining effective engine cooling.
Implementation Method 1
an induction voltage generated in a coil of a current-off phase of the three phase motor is compared with a reference voltage, and zero crossing of the induction voltage is detected
Data Source
AI summary
In a brushless motor control device, a microcontroller determines a current-on phase of a motor based on zero crossing detected by a position detection circuit, and the inverter circuit generates a voltage for current-on to the determined current-on phase. In a case in which zero crossing has been successively detected plural times, in a phase that was switched from the current-on phase to a current-off phase, in a PWM control cycle after a predetermined masking period, the microcontroller controls to interrupt current to coils of all phases of the motor body. In a state in which current-on has been interrupted, the microcontroller determines the current-on phase based on zero crossing detected in one of the three phases, the inverter circuit generates the voltage for current-on for the determined current-on phase and restarts current-on to the coils.