BLDC Phase Current Reconstruction Without Real-Time Trigonometry
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Solution Overview
Problem
Existing motor drive systems for brushless DC (BLDC) motors face challenges in efficiently reconstructing phase currents for field-oriented control due to the high processing power requirements of trigonometric calculations and the need for additional components, which increase physical space and system cost.
Innovation Solution
A half-bridge module with an internally sensed phase current sense signal is used, coupled with reference tables indexed by the stator current angle, to reconstruct phase currents, reducing processing time and external component count.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If trigonometric calculations are used for phase current reconstruction, then field-oriented control accuracy is improved, but processing time increases
Solution Approach 1:
The patent pre-calculates and stores current magnitude values in lookup tables before runtime. During operation, the controller simply retrieves pre-computed values based on measured current and angle, eliminating real-time trigonometric calculations while maintaining control accuracy.
Solution Approach 2:
The patent creates a simplified copy of the complex trigonometric relationship by storing pre-computed current magnitude values in lookup tables. This tabular representation replicates the mathematical relationship without requiring actual trigonometric computations during control execution.
2Measurement precision
If additional components are added for current sensing, then measurement capability is improved, but device complexity increases
Solution Approach 1:
The patent makes the existing current sense amplifier serve multiple functions: it provides both the original current measurement function and additional phase current reconstruction data. By utilizing the amplifier during both active and inactive switch states, the system extracts maximum information from a single component.
Solution Approach 2:
The system uses its own existing current sense amplifier to provide reconstruction data for all three phases, rather than requiring separate dedicated sensors for each phase. The amplifier essentially serves itself by providing data that can be processed to reconstruct complete three-phase current information.
Data Source
AI summary
A system controller for a motor drive system comprising a phase current reconstructor configured to perform operations. The operations comprise receiving a stator current angle and a plurality of phase current sense signals from a plurality of respective devices that in operation drive the motor drive system, selecting, based on the received stator current angle, a reference table from among a plurality of reference tables that store reconstruction scaling factors for respective phase currents, obtaining, from the selected reference table, respective reconstruction scaling factors for the respective phase currents, generating, from the obtained reconstruction scaling factors, respective reconstructed phase current magnitude values for the plurality of devices, and outputting the reconstructed phase current magnitude values.