Motor Drive Device Reverse Current Detection
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Solution Overview
Problem
Existing motor drive technologies experience a rise in power supply voltage due to motor current flowing back to the power supply during the synchronous rectifier period, leading to potential device damage and requiring additional components like capacitors or zener diodes for protection, which increase size and cost.
Innovation Solution
A motor drive device and method that includes a reverse current detection unit to sense changes in motor current direction during the regeneration state, allowing for control of the drive signal logic level to prevent power supply voltage rises, eliminating the need for external protection devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If synchronous rectifier control is used to reduce loss and improve efficiency, then energy efficiency is improved, but power supply voltage rises due to motor current backflow
Solution Approach 1:
The control unit interrupts synchronous rectifier control before the regeneration period ends when it detects a predetermined relationship between motor current and back electromotive force. This preliminary interruption prevents motor current from flowing back to the power supply, thereby preventing power supply voltage rise while maintaining the energy efficiency benefits of synchronous rectifier control during the effective period.
Solution Approach 2:
The control unit continuously monitors the relationship between motor current and back electromotive force during the regeneration period. Based on this feedback, the control unit dynamically adjusts the control strategy by interrupting synchronous rectifier control when the monitored parameters indicate impending current backflow, thus preventing power supply voltage rise while maximizing energy efficiency.
2Reliability
If external protection devices like capacitors or zener diodes are added to prevent power supply voltage rise, then reliability is improved, but device complexity and cost increase
Solution Approach 1:
The motor drive device uses its own control unit and existing sensors to monitor motor current and back electromotive force, and automatically interrupts synchronous rectifier control to prevent power supply voltage rise. This self-service approach eliminates the need for external protection devices like capacitors or zener diodes, maintaining reliability while reducing device complexity and cost.
Solution Approach 2:
The invention extracts the protection function from external hardware components and implements it through software control logic within the control unit. By taking out the need for physical protection devices and replacing them with intelligent control, the system achieves the same protective effect with fewer components, reducing complexity and cost.
3Loss of energy
If the regeneration period is extended to fully utilize synchronous rectifier control, then energy efficiency is improved, but the risk of motor current backflow and power supply voltage rise increases
Solution Approach 1:
The control unit calculates and interrupts synchronous rectifier control at a timing point before the regeneration period fully ends, based on a predetermined relationship between motor current and back electromotive force. This preliminary action extends the effective regeneration period as much as possible while maintaining a safety margin to prevent current backflow, thus optimizing both energy efficiency and reliability.
Solution Approach 2:
The control unit dynamically adjusts the duration of synchronous rectifier control based on real-time monitoring of motor current and back electromotive force. Rather than using a fixed regeneration period, the system adaptively extends or interrupts control based on actual operating conditions, maximizing energy recovery while preventing current backflow and power supply voltage rise.
Data Source
AI summary
A reverse current detection unit detects the direction of the motor current during the synchronous rectifier period based on the polarity of the on voltage of a switching device contained in the motor current path, and outputs a reverse current detection signal representing the result of this detection to the PWM control unit. Change in the output of the PWM control unit that generates the drive signal for a particular switching device in the drive unit is controlled based on the reverse current detection signal and the energizing pattern of the drive unit is changed when motor current is detected in the synchronous rectifier period to be flowing in the opposite direction as in the urging period. The flow of motor current to the power supply is thus reduced and a rise in the power supply voltage can be prevented.