A bidirectional active-clamped (AC) buck-boost converter is a type of power electronic circuit used for voltage conversion and energy transfer between a source and a load. It combines the functionalities of both a buck converter (step-down) and a boost converter (step-up) while incorporating an active-clamping mechanism to manage voltage spikes and reduce stress on components.
The primary principle behind a bidirectional AC buck-boost converter involves the use of two power switches (usually MOSFETs) and two diodes, along with a clamping capacitor and an inductor. The converter can operate in two modes: buck mode (step-down) and boost mode (step-up), allowing it to regulate the output voltage within a certain range regardless of whether the input voltage is higher or lower than the desired output voltage.
Here's how the bidirectional AC buck-boost converter works:
Buck Mode (Step-Down):
In this mode, the input voltage is higher than the desired output voltage. The upper power switch (MOSFET) is turned on, allowing current to flow from the input source through the inductor and load. The lower diode conducts, providing a path for the current to circulate. The clamping capacitor stores the energy from the inductor's leakage inductance and absorbs voltage spikes. This prevents the voltage across the lower switch from exceeding the input voltage, thus reducing stress on the switch.
Boost Mode (Step-Up):
In this mode, the input voltage is lower than the desired output voltage. The lower power switch (MOSFET) is turned on, allowing current to flow from the load through the inductor. The upper diode conducts, providing a path for the current to circulate. The clamping capacitor now helps maintain a smooth flow of energy by releasing the stored energy into the load. This prevents the voltage across the upper switch from dropping below zero, thus protecting the switch.
During transitions between buck and boost modes, the active-clamping mechanism is critical. When switching between modes, both power switches are off briefly. At this point, the energy stored in the inductor's magnetic field needs a path to dissipate. The clamping capacitor provides this path, ensuring a smooth transition and preventing voltage spikes that could damage components.
In summary, the bidirectional active-clamped buck-boost converter is a versatile circuit that enables efficient voltage conversion and energy transfer between a source and a load. Its ability to switch between buck and boost modes and its active-clamping mechanism help maintain stable and controlled voltage levels, while also protecting the switches and other components from excessive voltage spikes or drops.