A bidirectional active-clamped (AC) flyback converter is a type of power electronic circuit used for bidirectional energy transfer between two energy storage elements, such as batteries or supercapacitors, and a common DC bus. It combines features of both the flyback converter and the active-clamped topology to achieve efficient energy conversion and reduced voltage stresses on the switching devices.
Here's an explanation of the principle behind a bidirectional active-clamped flyback converter:
Basic Flyback Converter Operation:
A flyback converter is a type of DC-DC converter that uses a transformer to transfer energy between the input and output sides. During the first half of the switching cycle (ON-time), energy is stored in the transformer's primary winding as magnetic energy. When the switch turns off, the energy is transferred to the secondary winding and then to the output.
Active Clamp Operation:
An active clamp circuit is employed to absorb the voltage spikes that occur across the primary switch (typically a semiconductor like a MOSFET) when it turns off. These voltage spikes, also known as "voltage ringing," can damage the switch and other components if not properly managed. The active clamp circuit usually consists of a clamp capacitor, a diode, and a secondary-side switch.
Bidirectional Energy Flow:
In a bidirectional AC flyback converter, the active clamp circuit is utilized for bidirectional energy flow. This means that the converter can transfer energy from the input to the output (step-up mode) and from the output to the input (step-down mode). This bidirectional capability is achieved by controlling the operation of the primary-side and secondary-side switches.
Principle of Operation:
During the step-up mode (energy transfer from input to output):
The primary switch (MOSFET) turns on, and energy is stored in the transformer's primary winding.
When the primary switch turns off, the energy is transferred to the secondary winding, and a voltage spike is generated.
The active clamp circuit comes into play, providing a path for the voltage spike through the clamp diode and the clamp capacitor. This action prevents excessive voltage stress on the primary switch and ensures efficient energy transfer.
During the step-down mode (energy transfer from output to input):
The secondary-side switch (usually a synchronous rectifier) turns on, allowing energy from the output to flow back to the input.
The active clamp circuit again absorbs any voltage spikes generated during the switch-off process.
The bidirectional active-clamped flyback converter can efficiently handle energy transfer in both directions while maintaining controlled voltage levels across the switches and ensuring reliable and stable operation.
In summary, a bidirectional active-clamped flyback converter combines the energy transfer capabilities of a flyback converter with the voltage spike absorption features of an active clamp circuit. This enables bidirectional energy flow while protecting the switching components and ensuring efficient power conversion.