Air Conditioner Dual-Relay Control for Back-EMF Inrush
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Solution Overview
Problem
Conventional air conditioners face malfunctions due to inrush currents generated by back electromotive forces during outdoor winds, which cannot be prevented by existing inrush-current prevention resistors, leading to potential malfunctions.
Innovation Solution
An air conditioner design incorporating an inrush-current prevention resistor, a first relay serially connected to it, a second relay in parallel, and control units to manage the relays' ON/OFF states, ensuring the second relay is activated only when power is supplied through the first relay, thereby preventing inrush currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an inrush-current prevention resistor is provided in the air conditioner, then inrush current can be suppressed during normal power supply, but when back electromotive force generates bus voltage during outdoor winds, the inrush current cannot be prevented and malfunctions occur
Solution Approach 1:
The control unit checks whether the first relay is in the ON state before turning ON the second relay. This preliminary check ensures that the second relay is only activated when power is being supplied through the first relay, preventing inrush current caused by back electromotive force during outdoor winds.
Solution Approach 2:
The control unit continuously monitors the state of the first relay and uses this feedback information to control the second relay. When the first relay is OFF, the control unit prevents the second relay from turning ON, thereby preventing inrush current. When the first relay is ON, the control unit allows the second relay to turn ON for normal operation.
2Speed
If the second relay is allowed to turn ON independently, then the air conditioner can respond quickly to power supply changes, but inrush current may flow when bus voltage is generated by back electromotive force
Solution Approach 1:
The control unit performs a preliminary check of the first relay's state before activating the second relay. This ensures that the second relay is only turned ON when it is safe to do so (i.e., when power is already being supplied through the first relay), preventing inrush current while maintaining quick response capability for legitimate power supply changes.
Solution Approach 2:
The control unit acts as an intermediary between the first relay and the second relay. It mediates the activation of the second relay by checking the state of the first relay, thereby preventing direct independent activation that would cause inrush current while still allowing quick response to valid power supply changes.
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 configuration effectively prevents malfunctions caused by inrush currents due to back electromotive forces from outdoor winds, allowing the air conditioner to operate normally without activating the breaker.
Implementation Method 1
an inrush-current prevention resistor that prevents inflow of an inrush current coming from an AC power supply
Implementation Method 2
a first relay serially connected to the inrush-current prevention resistor; a second relay connected in parallel to the inrush-current prevention resistor and the first relay
Implementation Method 3
when an outside wind occurs, a bus voltage is generated due to a back electromotive force
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
An object is to provide an air conditioner that can prevent malfunctions due to an inrush current, where the air conditioner includes an inrush-current prevention resistor 9 that prevents inflow of an inrush current from an AC power supply 3, a relay-a operation unit 6 as a first relay that is serially connected to the inrush-current prevention resistor 9, a relay-b operation unit 8 as a second relay that is connected in parallel to the inrush-current prevention resistor 9 and the relay-a operation unit 6 as the first relay, an indoor control unit 21 that controls ON and OFF of the relay-a operation unit 6 as the first relay, and an outdoor control unit 18 that controls ON and OFF of the relay-b operation unit 8 as the second relay. When power is being supplied from the AC power supply 3 via the relay-a operation unit 6 as the first relay, the outdoor control unit 18 turns ON the relay-b operation unit 8 as the second relay.