Sensorless BLDC Startup Control Using Interphase Current Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Sensorless three-phase brushless DC motors face challenges in generating high torque from a stationary state, particularly in applications requiring high loads, such as power tools, due to issues like cogging torque and the inability to detect rotor position without a Hall sensor.
Innovation Solution
A semiconductor device controls a drive circuit by detecting current flow through the motor phases and determining an energization pattern based on interphase current differences, enabling high-torque operation by sequentially flowing wave detection currents between phases to determine an appropriate energization pattern for initial driving.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a sensorless motor is used to downsize and reduce cost, then device complexity and cost are reduced, but the ability to detect rotor position at stationary state is lost
Solution Approach 1:
The patent replaces the mechanical Hall sensor system with an electrical measurement system. Instead of using a physical sensor to detect rotor position, the system uses a detection circuit to measure current flow through the motor phases and calculates interphase current differences to determine rotor position electrically, thereby eliminating the need for mechanical sensors.
Solution Approach 2:
The patent introduces an intermediary measurement approach by using current detection as a mediator to indirectly determine rotor position. The detection circuit measures current flow between phases, and the controller calculates interphase current differences to infer rotor position information without direct mechanical contact or sensors.
2Power
If wave detection current is applied to determine energization pattern, then torque output is improved, but energy consumption increases
Solution Approach 1:
The patent applies preliminary action by performing rotor position detection and energization pattern determination before the motor actually starts rotating. The wave detection current is applied briefly in a stationary state to establish the correct energization pattern, enabling high-torque startup without continuous energy consumption during operation.
Solution Approach 2:
The patent uses periodic action by applying wave detection currents in a sequential, periodic manner across different motor phases. The detection circuit applies currents alternately to different phase combinations (UV, VW, WU phases) to measure interphase current differences, allowing comprehensive position detection through periodic measurement cycles.
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 sensorless motors to achieve equivalent torque to sensor-equipped motors by accurately determining the energization pattern, allowing for high-torque operation from a stationary state.
Implementation Method 1
the semiconductor device controls an energization pattern in such a way that a wave detection current sequentially flows from the drive circuit to a first interphase between the first phase and the second phase, a second interphase between the second phase and the third phase, and a third interphase between the third phase and the first phase
Data Source
AI summary
The semiconductor device includes: a current detection circuit configured to detect a current flowing through a three-phase motor by driving of a drive circuit; and a controller configured to control the drive circuit, based on the detected current. The controller is configured to control, when the three-phase motor is stationary, an energization pattern in such a way that a wave detection current sequentially flows from the drive circuit to each phase of the three-phase motor, to obtain, from the wave detection current detected by the current detection circuit, a first, a second and a third interphase current differences, each of which is a difference among wave detection currents flowing in directions opposite to one another, to determine the energization pattern based on a magnitude relationship among the first, the second and the third interphase current differences.