BLDC Motor Phase Shift Circuit Using Shared Low-Pass Filter
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Solution Overview
Problem
Conventional BLDC motor control circuits require multiple resources, including three comparators and three tunable low-pass filters, which can be resource-intensive, especially in programmable devices, and the phase delay is undesirably dependent on pulse width modulation duty cycle rather than rotation speed.
Innovation Solution
A circuit using two instrumentation amplifiers, two tunable low-pass filters, a summing circuit, and three zero-crossing detectors to generate phase-shifted signals for BLDC motor control, allowing for a reduced number of hardware resources and a phase shift that depends solely on motor rotation speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional BLDC motor control circuits use three comparators and three tunable low-pass filters to generate phase-shifted signals, then the phase shifting function is achieved, but the hardware resource consumption increases
Solution Approach 1:
The patent combines multiple filter functions into a single shared low-pass filter resource. Instead of using three separate tunable low-pass filters, the invention implements one filter that is sequentially configured to process different phase signals, thereby reducing hardware resource consumption while maintaining the phase shifting function.
Solution Approach 2:
The low-pass filter is designed to serve multiple functions by being reconfigurable. The same filter hardware is used to process back-EMF signals from different motor phases at different times, making a single component perform the work of what would traditionally require three separate filters.
2Device complexity
If conventional circuits use fixed threshold comparators with reference voltage set to half of supply voltage, then the circuit implementation is simple, but the phase delay becomes dependent on pulse width modulation duty cycle rather than rotation speed
Solution Approach 1:
The reference voltage is changed from a fixed value to a dynamic value that varies with motor rotation speed. The threshold comparator now uses a reference voltage that is proportional to the back-EMF signal amplitude, which automatically adjusts with speed, thereby decoupling the phase delay from PWM duty cycle dependencies.
Solution Approach 2:
The reference voltage parameter is changed from a constant half-supply-voltage value to a variable parameter that scales with the back-EMF amplitude. This parameter change allows the comparator to maintain proper phase detection across different operating conditions without being influenced by PWM duty cycle variations.
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
The improved circuit achieves optimal motor control with reduced resource usage and phase shift independence from pulse width modulation duty cycle, ensuring consistent performance across varying rotation speeds.
Implementation Method 1
The roll off frequency 380 is selected in such way to provide an approximately 30 degree phase shift at the selected rotation speed
Implementation Method 2
The back-EMF signals are signals generated by the rotor permanent magnet while it is spinning which have a force in the opposite direction of that in which the rotor is spinning
Data Source
AI summary
Disclosed is a controller circuit, comprising a plurality of sense inputs, an instrumentation amplifier block having inputs coupled to the plurality of sense inputs, a filter block coupled to the instrumentation amplifier block, a sum function coupled to the filter block, and a crossing detector block coupled to the filter block and the sum function. A method of controlling motor signals is further described.