Motor Drive Device Current Variation Restriction
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Solution Overview
Problem
Motor drive devices experience current variations when switching between synchronous and asynchronous rectification controls, which can affect steering performance in electric power-steering equipment, leading to changes in steering or driver feedback.
Innovation Solution
A motor drive device with a drive circuit unit featuring bridge-connected switching elements and parallel free wheel diodes, along with a controller that performs synchronous or asynchronous rectification control and includes a variation restriction portion to minimize current changes during state switches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If synchronous rectification control is performed, then power loss is reduced, but current variation occurs when switching between control modes
Solution Approach 1:
The control device performs preliminary action by adjusting the PWM duty cycle before switching between synchronous and asynchronous rectification control modes. When transitioning to asynchronous rectification control, the PWM duty cycle is increased to compensate for the loss of rectification efficiency, thereby maintaining stable motor current and preventing current variation that would affect steering performance.
Solution Approach 2:
The invention applies parameter changes by dynamically adjusting the PWM duty cycle parameter based on the rectification control mode. The control device changes the PWM duty cycle from a first value during synchronous rectification control to a second value (higher than the first) during asynchronous rectification control, thereby compensating for efficiency differences and maintaining current stability.
2Adaptability or versatility
If synchronous rectification control is switched to asynchronous rectification control, then adaptability is improved, but steering performance deteriorates due to current change
Solution Approach 1:
The control device maintains reliability during mode transitions by changing the PWM duty cycle parameter. When switching to asynchronous rectification control, the PWM duty cycle is increased to compensate for the lower rectification efficiency, ensuring that the motor current remains stable and steering performance is not affected.
Solution Approach 2:
The control device uses feedback by continuously monitoring the motor current and adjusting the PWM duty cycle accordingly. When asynchronous rectification control is activated, the system detects the current trend and increases the PWM duty cycle to maintain the target current level, thereby preserving steering performance through closed-loop control.
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
The solution reduces current variations caused by switching between rectification controls, thereby stabilizing steering performance and driver feedback in electric power-steering applications.
Implementation Method 1
In the PWM control, while one of the switching elements is turned off, back electromotive force arises in a motor coil
Implementation Method 2
While one of the switching elements is turned off, back electromotive force arises in a motor coil, and current flows in a free wheel diode disposed parallel to the other switching element
Implementation Method 3
In the synchronous rectification control, while the current flows into the free wheel diode, a switching element having a low on-resistance and connected in parallel with the free wheel diode is made conducted
Data Source
AI summary
A motor drive device includes: a drive circuit unit having a plurality pair of switching elements and a plurality pair of free wheel diodes connected in parallel to the plurality pair of switching elements respectively; and a controller that turns on/off the switching elements. The controller performs a synchronous rectification control in which at least one pair of the switching elements is complementarily turned on/off, or performs an asynchronous rectification control in which the synchronous rectification control is not performed. The controller has a variation restriction portion that restricts a variation in current that is caused by a switch from one of the synchronous rectification control and the asynchronous rectification control to the other.