BLDC Phase Current Reconstruction Using Angle Lookup Tables
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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 (FOC) due to the high processing power requirements of trigonometric calculations, which are not feasible with typical microcontrollers, and the use of external components increases physical space and cost.
Innovation Solution
A half-bridge module with an internally sensed phase current sense signal and reference tables for phase current reconstruction, reducing the need for external components and processing time by utilizing patterns in calculation results to index preloaded tables based on stator current angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If trigonometric calculations are used for phase current reconstruction, then measurement precision is improved, but processing time increases significantly
Solution Approach 1:
The patent pre-calculates and stores reconstruction scaling factors in lookup tables before operation. During runtime, the system only needs to perform simple table lookups and multiplications rather than computing complex trigonometric functions, thereby maintaining high precision while dramatically reducing processing time from 836.63 μs to approximately 2.63 μs
Solution Approach 2:
The patent creates a simplified copy of the complex trigonometric calculation process by storing pre-computed scaling factors in lookup tables. Instead of executing the original complex algorithm, the system uses these pre-computed values with simple multiplication operations to achieve the same reconstruction accuracy with minimal processing overhead
2Measurement precision
If external components are used for current sensing, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent merges the current sensing function into the half-bridge module itself by utilizing the existing low-side power switch and its drain current. The phase current sense signal is obtained internally from the half-bridge module without requiring separate external current sensors, thereby reducing component count while maintaining measurement capability
Solution Approach 2:
The low-side power switch in the half-bridge module serves dual purposes: it functions as a power switching device and simultaneously acts as a current sensor. The drain current of this switch provides the phase current sense signal, eliminating the need for dedicated external current sensing components and reducing overall system complexity
3Measurement precision
If traditional current sensing methods are used, then measurement precision is improved, but power loss increases
Solution Approach 1:
The system uses its own internal components (the low-side power switch and its drain current) to perform current sensing, eliminating the need for separate external current sensors that would consume additional power. The existing power switch serves the dual purpose of power control and current measurement, reducing overall power loss
Data Source
AI summary
A controller for a motor drive system comprises a stator current angle estimator, a phase current reconstructor, and a control signal generator. The phase current reconstructor is configured to receive a first phase current sense signal representative of a phase current of a first driver device, during a time when information about a phase current of a second driver device is unavailable from a second phase current sense signal. The phase current constructor is further configured to determine a scaling factor based on a first stator current angle estimate computed by the stator current angle estimator, and to reconstruct a value of the phase current of the second driver device through scaling the first phase current sense signal according to the scaling factor. The stator current angle estimator is further configured to compute a second stator current angle estimate based on the reconstructed value.