Brushless DC Motor Control System Using Resultant Current Sensor
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Solution Overview
Problem
Current control systems for three-phase square-wave brushless DC permanent-magnet motors face challenges in achieving accurate current closed-loop control due to the complexity and unreliability of traditional methods, which often result in significant deviations in torque control, leading to the adoption of more complicated and costly AC servomotors in high-performance applications.
Innovation Solution
A brushless DC motor control system that employs a simpler resultant current sensor to completely and continuously sample the three-phase current during motor operation, including freewheeling, and utilizes a single current closed-loop regulator, integrated with a linear Hall element and a modified inverting circuit with switch tubes and freewheel diodes, to enable precise current feedback and control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If three independent current sensors and three independent current regulators are used to achieve current closed-loop control, then current control accuracy is improved, but device complexity increases and reliability decreases
Solution Approach 1:
The patent combines three independent current sensors into a single resultant current sensor that measures the sum of three-phase currents. Similarly, three independent current regulators are merged into a single current regulator. This merging reduces device complexity while maintaining current control accuracy through the relationship that the sum of three-phase currents equals the bridge arm current.
Solution Approach 2:
The single resultant current sensor serves multiple functions by simultaneously providing current measurement information for all three phases. The single current regulator universally controls all three-phase currents through the bridge arm current, eliminating the need for separate regulation circuits for each phase.
2Device complexity
If bridge arm current sampling is used to simplify the control circuit, then device complexity is reduced, but measurement precision deteriorates due to inability to accurately sample actual motor winding current
Solution Approach 1:
The patent introduces a feedback mechanism where the resultant current sensor continuously monitors the bridge arm current, and this information is fed back to the single current regulator. The regulator uses this feedback to adjust the switching signals, ensuring that the actual motor winding current is accurately controlled despite using simplified bridge arm sampling.
Solution Approach 2:
The patent uses the relationship between bridge arm current and motor winding current as an intermediary. By measuring the bridge arm current (which is easier to access) and using the known electrical relationships in the three-phase system, the system indirectly obtains accurate information about the actual motor winding current without directly sampling each phase.
3Measurement precision
If AC servomotor or sine brushless permanent-magnet DC motor is employed instead of square-wave brushless permanent-magnet DC motor to achieve high-performance servo control, then current closed-loop control performance is improved, but device complexity and cost increase
Solution Approach 1:
The patent changes the control approach by applying current closed-loop control techniques traditionally used for AC servomotors and sine brushless motors to square-wave brushless motors. By modifying the control parameters and using the resultant current sensing method, the system achieves high-performance servo control with the simpler and more cost-effective square-wave motor topology.
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
This solution significantly enhances the dynamic and static performance of the motor, allowing for accurate current control and reducing costs by up to 50% while increasing force index by 33%, making it suitable for high-performance servo control systems like numerical control machines and automation production lines.
Implementation Method 1
a sensing element that outputs the current sensing result according to a magnetic flux change of the iron core is mounted on the iron core
Implementation Method 2
two sampling coils L1 and L2 having the same number of turns, which are wound around the same iron core
Data Source
AI summary
The present invention relates to a control technology of a three-phase DC motor. In order to resolve a problem in the prior art that the good current closed-loop control has not been realized on a three-phase square-wave brushless DC motor, the present invention provides a brushless DC motor control system, wherein cathodes of freewheel diodes D1, D3 and D5 are independent of input terminals of their respective switch tubes and connected in parallel to a sampling coil L1, and anodes of freewheel diodes D4, D6 and D2 are independent of output terminals of their respective switch tubes and connected in parallel to a sampling coil L2. The present invention can use a single resultant current sensor to completely and continuously sample the three-phase current existing during the motor is on and performs current freewheel, and perform the continuous closed-loop control on the three-phase current with a single current closed-loop regulator, thereby increasing dynamic and static indexes of the motor significantly.