Single-Phase AC Motor Control Circuit for Dryer
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Solution Overview
Problem
Existing single-phase AC motor control circuits for dryers rely on mechanical centrifugal switches, which generate arc sparks, complicate motor design, increase size and material costs, and result in imperfect control and prolonged starting times due to simultaneous powering of starting and main windings during the starting phase.
Innovation Solution
A single-phase AC motor control circuit utilizing bidirectional triode thyristors BCR1 and BCR2, interlocked drive circuits, and a hysteresis comparison circuit to independently control the starting winding and heated strip, eliminating arc sparks and simplifying motor design, allowing precise control and efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mechanical centrifugal switch is used for starting control, then the starting winding can be switched on/off, but arc sparks are generated during switching and the work life is reduced
Solution Approach 1:
The patent replaces the mechanical centrifugal switch with an electronic control system using triode thyristors (BT1, BT2) controlled by comparison circuits. This substitution eliminates mechanical contact and arc spark generation while achieving the same starting winding control function through electronic switching based on motor speed detection.
2Ease of operation
If a mechanical centrifugal switch is disposed in the motor, then starting control is achieved, but the structure becomes complex and size increases
Solution Approach 1:
The mechanical centrifugal switch is replaced with an electronic control circuit comprising triode thyristors, comparison circuits, and detection windings. This electronic system achieves starting control without requiring mechanical moving parts inside the motor, thereby simplifying the motor structure and reducing its size.
Solution Approach 2:
The patent introduces an intermediary detection winding and comparison circuit that senses motor speed and controls the triode thyristors accordingly. This intermediary system enables starting control without direct mechanical components, simplifying the overall motor design.
3Productivity
If starting winding and main winding are simultaneously powered up, then motor starting is initiated, but large current creates heavy workload on power system and prolongs starting time
Solution Approach 1:
The patent implements periodic control of the starting winding through triode thyristors that are switched on and off based on motor speed detection. The starting winding is energized in periodic pulses during the starting phase, then switched off when the motor reaches a certain speed, thereby reducing overall current demand and shortening starting time compared to continuous simultaneous powering.
Solution Approach 2:
The patent uses a feedback mechanism where the detection winding monitors motor speed and feeds this information to the comparison circuit, which then controls the triode thyristors to adjust starting winding power. This feedback control optimizes the starting process by reducing current when the motor approaches operating speed, decreasing power system workload and starting time.
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 provides reliable, efficient, and precise control of the motor, reduces motor size and material costs, and prevents arc sparks, ensuring normal operation and extended lifespan by using bidirectional triode thyristors and interlocked drive circuits.
Implementation Method 1
a bidirectional triode thyristor BCR1, and a starting capacitor, the bidirectional triode thyristor BCR1 is serially connected to a starting winding of a motor of a dryer
Implementation Method 2
the bidirectional triode thyristor BCR2 is serially connected to an electrically heated strip, and then to the utility power AC input
Implementation Method 3
the voltage comparison circuit employs a hysteresis comparison circuit
Data Source
AI summary
A single-phase AC motor control circuit for a dryer, including a starting control unit, a first drive circuit, a bidirectional triode thyristor BCR1, a second drive circuit, and a bidirectional triode thyristor BCR2. The bidirectional triode thyristor BCR1 is serially connected to a motor starting winding, and a starting capacitor, and then to a utility power AC input. The starting control unit is connected to a control end of the bidirectional triode thyristor BCR1 via the first drive circuit. The bidirectional triode thyristor BCR2 is serially connected to an electrically heated strip, and then to the utility power AC input. The starting control unit is connected to a control end of the bidirectional triode thyristor BCR2 via the second drive circuit. The first drive circuit is interlocked with the second drive circuit.