BLDC Motor Controller ZCP Detection via PWM Synchronization
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing sensor-less detection methods for 3-phase brushless DC motors face challenges in accurately detecting zero crossing points (ZCPs) of back electromotive forces (BEMFs) at high speeds, often resulting in incorrect ZCP signals due to phase delay from low-pass filters and transient states, limiting motor rotating speed.
Innovation Solution
A controller with a PWM signal generation unit, analog to digital converter, synchronization and extraction unit, and judgment unit that operates in synchronization with PWM signals, using wait and delay instructions to extract stable BEMF values and generate accurate ZCP signals without extra hardware, allowing for precise commutation operations and high-speed motor operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If sensor-less detection is used to avoid position sensor, then cost and space are reduced, but measurement precision of ZCP detection deteriorates at high speeds
Solution Approach 1:
The patent applies dynamics by making the detection system adaptive to varying motor speeds. The controller dynamically adjusts the detection timing and uses synchronous detection with PWM signals to maintain ZCP detection precision across different operating speeds, transforming a static detection approach into a dynamic one that responds to speed changes.
Solution Approach 2:
The patent changes the parameter of detection timing by introducing synchronized detection windows aligned with PWM cycles. By adjusting when measurements are taken within each PWM period and using delay instructions to skip transient states, the system maintains measurement precision without requiring additional hardware.
2Object-affected harmful factors
If low-pass filter is used to filter PWM chopping signals, then signal noise is reduced, but phase delay occurs causing incorrect ZCP signals
Solution Approach 1:
The patent applies preliminary action by proactively identifying and skipping transient states before they corrupt the measurement. The controller uses delay instructions to wait for the BEMF signal to stabilize after PWM transitions, performing the detection operation at the optimal moment before transient effects occur, thus preventing rather than correcting the problem.
Solution Approach 2:
The patent applies skipping by deliberately bypassing the transient state periods in the detection process. The synchronous detection mechanism skips over the unstable portions of the signal waveform that occur during PWM transitions, rushing through the problematic regions to reach the stable measurement window where accurate ZCP detection can occur.
3Productivity
If detection is performed during PWM duty-on period, then ZCP detection coverage is improved, but transient states cause incorrect judgment
Solution Approach 1:
The patent applies preliminary action by preparing the detection system to identify and skip transient states before performing the actual ZCP measurement. The synchronous detection mechanism is pre-synchronized with PWM signals, allowing it to anticipate when stable measurement windows will occur within each duty cycle and position measurements accordingly.
Solution Approach 2:
The patent applies feedback by using the known PWM signal timing as a reference to guide the detection process. The controller continuously monitors PWM cycle timing and uses this feedback to synchronize BEMF sampling, adjusting measurement timing based on the rhythmic pattern of PWM switching to maintain reliable detection throughout the duty-on period.
4Measurement precision
If additional hardware circuit is added for accurate ZCP detection, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent applies mechanics substitution by replacing potential additional hardware filtering circuits with software-based synchronous detection algorithms. Instead of adding physical low-pass filters or complex analog circuitry, the invention uses digital signal processing techniques implemented in the controller's firmware to achieve the same noise rejection and measurement accuracy.
Solution Approach 2:
The patent applies self-service by enabling the existing controller to perform accurate ZCP detection using its own existing resources - the PWM generation capability and digital processing units already present in the system. The synchronous detection mechanism leverages the controller's inherent timing signals rather than requiring external reference inputs or additional measurement hardware.
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 reliable and accurate detection of ZCPs, allowing for efficient and precise commutation operations at high speeds without additional hardware, reducing motor cost and complexity, and eliminating phase sequence misses.
Implementation Method 1
The sensor-less detection detects the position of the rotor, according to a back electromotive force (referred to as BEMF, hereinafter) induced when the motor is rotating. The BEMF is a terminal voltage induced in an unexcited (floating) winding by change of a magnetic field when the rotor of the motor is rotating.
Data Source
AI summary
The present invention discloses a 3-phase brushless DC motor controller, which comprises: a unit for generating a PWM signal; an ADC for converting a back electromotive force (BEMF) signal from an analog form into a digital form; a synchronization and extraction unit operating in synchronization in part with the PWM signal for extracting the digital BEMF signal to obtain a corresponding ZCP signal; and a unit for judging whether a commutation operation is to be performed according to a change of the corresponding ZCP signal. A wait instruction and a delay instruction help to accurately acquire the digital BEMF signal.