Hybrid charger and inverter system
An AC-AC converter can include a stack of four switches. An input of the converter can be coupled across the stack of four switches, and an output of the converter can be taken from first terminal coupled to a connection point of first and second switches of the stack and a second terminal coupled to a connection point of third and fourth switches of the stack. The converter can further include a controller that operates the switches such that during a positive half cycle of an AC input voltage, the first and second switches are operated with an alternating 50% duty cycle and the third and fourth switches are constantly on, and during the negative half cycle of the AC input voltage, the third and fourth switches are operated with an alternating 50% duty cycle and the first and second switches are constantly on.
1. An AC-AC converter comprising:
a stack of four switching devices, wherein an input of the AC-AC converter is coupled across the stack of four switching devices and an output of the AC-AC converter is taken from first terminal coupled to a connection point of first and second switching devices of the stack and a second terminal coupled to a connection point of third and fourth switching devices of the stack; and
a controller that operates the switching devices such that:
during a positive half cycle of an AC input voltage, first and second switching devices of the stack are operated with an alternating 50% duty cycle and third and fourth switching devices of the stack are constantly on; and
during the negative half cycle of the AC input voltage, the third and fourth switching devices of the stack are operated with an alternating 50% duty cycle and the first and second switching devices of the stack are constantly on;
wherein:
during the positive half cycle, the duration of the on-times of the first and second switching devices determine the magnitude of the AC voltage between the first and second terminals; and
during the negative half cycle, the duration of the on times of the third and fourth switching devices determine the magnitude of the AC voltage between the first and second terminals.
2. The AC-AC converter of claim 1 further comprising first and second series-connected input capacitors coupled across the input of the AC-AC converter, with a connection point of the series-connected input capacitors coupled to a connection point of the second and third switching devices.
3. The AC-AC converter of claim 1 further comprising at least one output filter inductor and at least one output filter capacitor coupled to the output of the AC-AC converter.
4. The AC-AC converter of claim 3 wherein the at least one filter inductor comprises a first filter inductor coupled between the first terminal and a load.
5. The AC-AC converter of claim 4 wherein the at least one filter inductor comprises a second inductor coupled between the second terminal and the load.
6. The AC-AC converter of claim 1 further comprising a resonant tank made up of at least one resonant capacitor and at least one resonant inductor, wherein the resonant tank facilitates zero voltage switching of the switching devices.
7. The AC-AC converter of claim 6 wherein the resonant tank is a series resonant circuit coupled between the first terminal and the second terminal.
8. The AC-AC converter of claim 6 wherein the resonant tank is a series resonant circuit coupled in parallel with the at least one output filter inductor.
9. A method performed by a controller of an AC-AC converter having a stack of four switching devices, wherein an input of the AC-AC converter is coupled across the stack of four switching devices and an output of the AC-AC converter is taken from first terminal coupled to a connection point of first and second switching devices of the stack and a second terminal coupled to a connection point of third and fourth switching devices of the stack, the method comprising:
during a positive half cycle of an AC input voltage:
operating first and second switching devices of the stack with an alternating 50% duty cycle; and
turning on and leaving on third and fourth switching devices of the stack; and
during a negative half cycle of the AC input voltage:
operating the third and fourth switching devices of the stack with an alternating 50% duty cycle; and
turning on and leaving on the first and second switching devices of the stack;
wherein:
during the positive half cycle, the duration of the on-times of the first and second switching devices determine the magnitude of the AC voltage between the first and second terminals; and
during the negative half cycle, the duration of the on times of the third and fourth switching devices determine the magnitude of the AC voltage between the first and second terminals.
10. The method of claim 9 wherein the switching devices are operated with zero voltage switching.