Electronic Relay for Single Phase Induction Motor Start Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Single phase induction motors face high start failure rates and reduced compatibility due to reliance on mechanical centrifugal switches and inefficient analog control circuits in existing electronic relays, which are prone to mechanical degradation and power inefficiency.
Innovation Solution
A method using a semiconductor switching device to control current in the start winding, detecting induced voltage proportional to rotor angular velocity, calculating its variation rate to determine maximum start torque, and turning off the device when the torque decreases, along with an electronic relay that includes a triac, induced voltage detection circuit, and a Micro Control Unit to manage start and restart operations based on voltage phase comparisons.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mechanical centrifugal switch is used to disconnect the start winding after motor startup, then the start torque can be effectively controlled, but the reliability deteriorates due to mechanical degradation from vibration and electrical abrasion
Solution Approach 1:
The patent replaces the mechanical centrifugal switch with an electronic relay system that uses a semiconductor switching device (triac) controlled by a control circuit. The control circuit monitors the induced voltage in the start winding and automatically turns off the triac when the motor reaches sufficient speed, eliminating mechanical moving parts while maintaining the start torque control function. This substitution resolves the contradiction by improving reliability through elimination of mechanical wear while managing device complexity through electronic control.
2Reliability
If an electronic relay with analog control circuit is used to control the triac gate, then the start winding current can be controlled, but the efficiency of internal power source circuit deteriorates due to high current consumption
Solution Approach 1:
The patent changes the control parameter from direct analog voltage control to monitoring the induced voltage in the start winding. The control circuit measures the induced voltage level, which naturally increases as motor speed increases, and uses this parameter to control the triac switching. This approach reduces power consumption because the control circuit draws minimal current for sensing compared to driving an analog control circuit, while maintaining reliable start control through the natural voltage buildup in the start winding.
3Adaptability or versatility
If a simple voltage level detection method is used to determine start completion, then the control circuit is simple, but the compatibility deteriorates because characteristics change according to motor standards and disposition conditions
Solution Approach 1:
The patent implements a feedback mechanism where the control circuit continuously monitors the induced voltage in the start winding during the starting process. By measuring how the induced voltage builds up as motor speed increases, the control circuit can determine when the motor has reached sufficient speed to disconnect the start winding. This feedback approach improves compatibility across different motor standards because it adapts to the actual motor performance characteristics rather than relying on fixed voltage thresholds, while the increased control circuit complexity is justified by the enhanced adaptability.
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 approach minimizes start failures, increases compatibility with various motor standards, and allows for quick and accurate restarts, correcting reverse runs and enabling momentary forward/reverse rotations while protecting the circuit.
Implementation Method 1
sensing voltage of a starting winding induced in driving the motor; detecting an induced voltage proportional to an angular velocity of a rotor from the start winding
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The present invention relates to an electronic relay for single phase induction motor, which model a start torque curve with an induced voltage to perform control in a programming scheme, and thus can minimize a start failure and increase compatibility in order for be applied to motors based on various standards. The electronic relay for single phase induction motor includes a triac, an induced voltage detection circuit, a window comparison circuit, and a Micro Control unit (MCU). The triac is connected between a start winding and start capacitor of the single phase induction motor to control (break or connect) a current flow of the start winding. The induced voltage detection circuit detects an induced voltage of the start winding proportional to an angular velocity of the motor. The window comparison circuit detects a both-end voltage of the triac to detect a zero-point voltage of a motor line voltage before start and to detect a zero-point current of a start winding current during start. The MCU turns on the triac at the zero-point voltage of the motor line voltage to begin starting according to a signal of the window comparison circuit, triggers a gate of the triac for a certain delay time at every zero-point current time of the start winding current to maintain a turn-on state of the triac according to the signal of the window comparison circuit during start, receives the induced voltage of the start winding from the induced voltage detection circuit to calculate a variation rate of the induced voltage proportional to an acceleration torque of the motor during start, checks that in which a start torque is the maximum with that in which an acceleration torque is the maximum, and turns off the triac when the acceleration torque begins decreasing.