Brushless Motor Current Control Across Phase Switching
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Solution Overview
Problem
When 120-degree square-wave drive is executed on a three-phase brushless motor, the motor current temporarily drops when the energized phases are switched, leading to oscillation and potential overcurrent or torque control failures.
Innovation Solution
A motor control apparatus and method that calculates a control current value based on current values detected before and after the switching of energized phases, using a response delay process to stabilize the motor current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If 120-degree square-wave drive is executed on a three-phase brushless motor, then the motor can operate in square-wave mode, but the motor current temporarily drops when energized phases are switched causing oscillation and potential overcurrent
Solution Approach 1:
The control unit calculates the control current value based on current values detected before and after switching of the energized phases. This preliminary calculation approach allows the system to anticipate and compensate for the current drop that occurs during phase switching, preventing oscillation and overcurrent before they occur.
Solution Approach 2:
The control unit uses feedback from the current sensor to detect the actual current flowing through the energized phases. By continuously monitoring the current before and after switching events and adjusting the control current value accordingly, the system maintains stable motor operation despite the inherent current drop during phase transitions.
2Speed
If detected current value is used directly for energization control, then the control system responds quickly to current changes, but motor current oscillation occurs leading to overcurrent and torque control failure
Solution Approach 1:
The control unit performs preliminary calculation of the control current value using current values detected before switching occurs. This allows the system to prepare the appropriate control current in advance, maintaining quick response while avoiding the oscillation that would result from directly using the detected current value during the switching transition.
Solution Approach 2:
The control current value calculated by the control unit acts as an intermediary between the raw detected current signal and the actual energization control. This intermediate calculation step filters out the harmful oscillations while preserving the essential current information needed for torque control, enabling both fast response and stable operation.
Data Source
AI summary
In one mode, a motor control apparatus and a motor control method according to the present invention acquire a detected signal of a current sensor that detects a current flowing through the energized phases of a three-phase brushless motor, and execute 120-degree square-wave drive on the three-phase brushless motor based on a control current value based on the detected signal. The motor control apparatus and motor control method calculate the control current value based on a current value detected by the current sensor before switching of the energized phases in the 120-degree square-wave drive and based on a current value detected by the current sensor after the switching. This configuration enables reduction of oscillation of a motor current.