AC Switch Current Cancellation for Surge-Free Power Transfer
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Solution Overview
Problem
In power supply devices with semiconductor switches, turning off the switch when current is flowing can generate surge voltages, leading to resonance phenomena due to stored energy in snubber circuits.
Innovation Solution
The power supply device includes a controller that manages the semiconductor switch and bidirectional power converter. When the AC power supply is normal, the controller turns on the semiconductor switch. During a power outage or circuit breaker opening, the controller controls the power converter to supply a current with an opposite phase to the semiconductor switch, ensuring no current flows when the switch is turned off.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a semiconductor switch is used in the AC switch to perform ON/OFF operation at high speed, then the switching speed is improved, but a surge voltage may be generated when the semiconductor switch is suddenly turned off
Solution Approach 1:
A snubber circuit is connected in parallel to the semiconductor switch to cushion the surge voltage generated when the switch is turned off. The snubber circuit absorbs the voltage spike through its capacitor and dissipates it through its resistor, protecting the semiconductor switch from damage.
Solution Approach 2:
The snubber circuit acts as an intermediary between the semiconductor switch and the circuit, absorbing and dissipating the surge voltage energy. This mediator prevents the direct transmission of harmful voltage spikes to other circuit components.
2Object-affected harmful factors
If a snubber circuit is connected in parallel to the semiconductor switch to prevent surge voltage, then the surge voltage is suppressed, but the energy stored in the snubber capacitor may flow through the voltage detector and cause magnetic saturation
Solution Approach 1:
The harmful energy stored in the snubber capacitor is extracted and redirected through the power converter to the power storage device instead of flowing through the voltage detector. This extraction prevents the energy from causing magnetic saturation in the voltage detector's inductance.
Solution Approach 2:
The energy that would otherwise be harmful (causing magnetic saturation) is converted into a beneficial function by routing it through the power converter to charge the power storage device. The harmful snubber capacitor discharge energy becomes a useful power source for the load during power outages.
3Productivity
If the semiconductor switch is turned off when current is flowing, then the switching operation is completed, but a resonance phenomenon may occur between the inductance and the snubber capacitor
Solution Approach 1:
The controller performs preliminary action by detecting the current flowing through the semiconductor switch and determining the optimal timing for turn-off. By switching at the zero-crossing point of the current waveform, the controller prevents the accumulation of energy that would cause resonance between the inductance and snubber capacitor.
Solution Approach 2:
The current detector provides feedback about the current flowing through the semiconductor switch to the controller. This feedback enables the controller to make informed decisions about the optimal switching timing, ensuring that the switch is turned off when current is zero to avoid resonance phenomena.
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 prevents surge voltages and resonance phenomena when the semiconductor switch is turned off, ensuring stable power supply to the load.
Implementation Method 1
a bidirectional power conversion circuit connected to the input terminal via the AC switch, a power storage device connected to the bidirectional power conversion circuit
Implementation Method 2
when there is energy stored in the snubber capacitor
Implementation Method 3
the energy stored in the snubber capacitor flows through the voltage detector, which may bring an inductance in the voltage detector to magnetic saturation
Implementation Method 4
The magnetic saturation of the inductance may cause a resonance phenomenon to occur between the inductance and the snubber capacitor
Data Source
AI summary
An AC switch that includes a semiconductor switch and a snubber circuit connected in parallel between a first terminal connected to an AC power supply via a circuit breaker and a second terminal connected to a load. The power converter is connected between a power storage device and the second terminal. The current detector detects a current flowing through the AC switch. When the AC power supply is normal, the controller turns on the semiconductor switch. When an open state of the circuit breaker is detected, the controller controls the power converter to supply a current having a phase opposite to that of the current detected by the current detector to flow through the semiconductor switch and supply the AC power to the load. The controller further turns off the semiconductor switch in response to that the amplitude of the current detected by the current detector is 0.