Motor Drive Circuit Low Speed Start Cogging Torque
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Solution Overview
Problem
Existing motor drive circuits face challenges in starting a single-phase motor at low speeds due to the large difference between maximum and minimum cogging torque levels, leading to failure in starting the motor when the drive voltage is low and the driving ratio is decreased, especially in single-phase motors.
Innovation Solution
A motor drive circuit that includes a drive voltage generation circuit, first and second pulse generation circuits, and a control circuit to generate drive signals with specific duty ratios, allowing for intermittent driving of the motor coil with a constant second duty ratio to initiate rotation and switching to a first duty ratio after a predetermined time to maintain speed, thereby overcoming the cogging torque limitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the drive voltage is decreased to minimize power consumption and noise, then the motor rotation speed is reduced, but the motor cannot start at low speed due to insufficient torque to overcome cogging torque
Solution Approach 1:
The patent applies dynamics by making the duty ratio variable rather than fixed. The duty ratio is dynamically adjusted based on the motor's rotational state: a higher duty ratio is used during startup to overcome cogging torque, and a lower duty ratio is used during normal operation to minimize power consumption. This dynamic adjustment resolves the contradiction between starting capability and energy efficiency.
Solution Approach 2:
The patent changes the parameter of duty ratio based on operating conditions. By switching between different duty ratio values (first duty ratio for startup, second duty ratio for operation), the system adapts to different operational requirements, enabling low-speed startup while maintaining low power consumption during normal operation.
2Object-generated harmful factors
If the drive voltage is low and driving ratio is decreased to reduce noise, then power consumption is minimized, but the torque for driving the motor cannot exceed the maximum level of cogging torque resulting in failure to start at low speed
Solution Approach 1:
The patent uses dynamic adjustment of the duty ratio to resolve the contradiction between noise reduction and starting capability. During startup, a higher duty ratio provides sufficient torque to overcome cogging torque and start the motor. Once the motor is running, a lower duty ratio maintains operation with reduced noise and power consumption.
Solution Approach 2:
The patent applies preliminary action by providing a higher duty ratio specifically during the startup phase before switching to normal operation. This preliminary high-torque action ensures the motor overcomes cogging torque and starts rotating, after which the system transitions to low-noise operation mode.
3Device complexity
If a single-phase motor is used, then device complexity is reduced, but the difference between maximum and minimum cogging torque levels is larger making starting at low speed more difficult
Solution Approach 1:
The patent compensates for the inherent disadvantage of single-phase motors by dynamically changing the duty ratio parameter. The control circuit switches between different duty ratio values to provide sufficient starting torque despite the larger cogging torque variation characteristic of single-phase motors, thereby maintaining starting capability without increasing mechanical complexity.
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 successful starting of the motor at low speeds by providing a start compensation function and soft start control, while maintaining a wider speed variance range compared to conventional PAM control methods, minimizing power consumption and noise.
Implementation Method 1
a cogging torque occurs by attraction or repulsion corresponding to the positional relation of the magnetic poles and the motor coil
Data Source
AI summary
The invention provides a motor with a low speed start function and a soft start function. The motor includes a first pulse generation circuit generating a first pulse signal of which a first duty ratio of one of logic levels is increased as a drive voltage corresponding the target rotation speed of the motor is increased, a second pulse generation circuit generating a second pulse signal of which a second duty ratio of one of logic levels is different from the first duty ratio, and a drive control circuit supplying a drive current to a motor coil at the second duty ratio in order to start the rotation of the motor that is stopping and supplying a drive current to the motor coil at the first duty ratio after a predetermined time passes from the start of the rotation of the motor in response to a rotation signal corresponding to the rotation of the motor.