Sensorless Speed Detection Using Bootstrap Voltage Comparison
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Solution Overview
Problem
Existing methods for detecting the speed of a Permanent Magnet Brushless Motor during rotation, especially during the Zero Vector phase when all phases are shorted, are ineffective as they lack current sensing due to no current flowing in the DC bus and absence of sensors in sensorless motors.
Innovation Solution
Detecting the voltage across a switch of a switching stage during the Zero Vector application to determine the current direction and frequency, using a high voltage gate driver integrated circuit (HVIC) with a bootstrap power supply to compare voltages and output signals indicating current sign and frequency, allowing motor speed determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If sensorless control is used to eliminate sensors, then device complexity and cost are reduced, but speed detection capability during Zero Vector phase is lost
Solution Approach 1:
The patent uses the bootstrap capacitor voltage as an intermediary signal to indirectly detect motor speed. Instead of directly measuring current or speed, the voltage across the bootstrap capacitor serves as a mediator that reflects the motor's operating state during Zero Vector phase, enabling speed detection without direct sensors.
Solution Approach 2:
The patent replaces physical sensors with an electrical measurement approach. By monitoring the voltage across the bootstrap capacitor and comparing it with a reference voltage, the system substitutes mechanical/sensor-based detection with an electrical field-based measurement method.
2Ease of operation
If Zero Vector is applied for braking, then motor control is improved, but current sensing becomes impossible due to no current flowing in DC bus
Solution Approach 1:
The bootstrap capacitor voltage serves as an intermediary that indirectly indicates current flow status in the motor phases during Zero Vector braking. By monitoring this voltage and comparing it with a reference, the system can infer current direction and frequency without direct current sensing.
Solution Approach 2:
The system implements feedback by continuously monitoring the bootstrap capacitor voltage and using it to determine motor speed and current transitions. This feedback mechanism allows the controller to adjust braking performance based on real-time motor state information.
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
Enables accurate speed detection of the motor during braking, ensuring safe stopping of washing machine drums by determining motor speed without sensors, even during Zero Vector conditions.
Implementation Method 1
a comparator circuit to periodically compare the voltage between the bootstrap power supply and low-side driver power supply with a threshold and to output a signal
Data Source
AI summary
According to one disclosed embodiment, a gate driver circuit for sensorless speed detection and driving a switching stage includes high side and low side switches series connected across a DC bus and having a switching node between the series switches, the gate driver having a bootstrap power supply for powering a high side driver driving the high side switch of the switching stage and a low side driver power supply, and further includes a comparator circuit to periodically compare the voltage between the bootstrap and low side driver power supplies with a threshold and to output a first signal, wherein the first signal indicates current sign and frequency.