Non-isolated inverting apparatus, control method thereof and photovoltaic system having the same

1. A non-isolated inverting apparatus, comprising:

a DC port comprising a first terminal and a second terminal;

an AC port comprising a first terminal and a second terminal;

five switches comprising a first switch, a second switch, a third switch, a fourth switch and a fifth switch, each of the switches having a first terminal, a second terminal and a third terminal,

wherein the first terminal of the first switch and the first terminal of the fifth switch are electrically coupled to the first terminal of the DC port, the second terminal of the second switch and the first terminal of the fourth switch are electrically coupled to the second terminal of the DC port and the second terminal of the AC port, the first terminal of the third switch and the second terminal of the first switch are electrically coupled to the first terminal of the AC port, and the second terminal of the third switch is electrically coupled to the second terminal of the fourth switch;

a first inductor electrically coupled between the first terminal of the second switch and the second terminal of the fifth switch;

a first capacitor electrically coupled between the first terminal of the second switch and the second terminal of the fourth switch; and

a free-wheeling element electrically coupled between the second terminal of the third switch and the second terminal of the fifth switch;

wherein the five switches are configured to be controlled via the third terminal respectively, according to control signals, so that the inverting apparatus are switched among a plurality of operating modes and transmit an active power or a reactive power to a power grid, and that in at least one of the operating modes, only one switch connected between the AC port and the DC port is turned on.

2. The non-isolated inverting apparatus according to claim 1 , wherein the inverting apparatus further comprises a filter circuit electrically coupled to the AC port and generating an output voltage, wherein the filter circuit comprises a filter inductor electrically coupled between the first terminal of the AC port and the output voltage, and a filter capacitor coupled in parallel to the output voltage.

3. The non-isolated inverting apparatus according to claim 1 , wherein during the positive half cycle, the first switch and the third switch are in a high-frequency switching state, turning on and off complementarily; the second switch is maintained in OFF state, and the fourth switch and the fifth switch are maintained in ON state.

4. The non-isolated inverting apparatus according to claim 1 , wherein during the negative half cycle, the first switch is maintained in OFF state, the second switch and the fourth switch are in a high-frequency switching state, turning on and off complementarily; the third switch is maintained in ON state, and the fifth switch is in a high-frequency switching state.

5. The non-isolated inverting apparatus according to claim 4 , wherein the fifth switch is turned on instantaneously when the second switch is turned off, and conduction time of the fifth switch equals to conduction time of the second switch.

6. The non-isolated inverting apparatus according to claim 1 , wherein the free-wheeling element comprises a controllable switching device or an uncontrollable switching device.

7. A photovoltaic system having the non-isolated inverting apparatus according to claim 1 , wherein the DC port is electrically coupled to at least one photovoltaic panel, and the AC port is electrically coupled to a power grid.

8. A method of controlling the non-isolated inverting apparatus according to claim 1 , comprising:

wherein during the positive half cycle, the first switch and the third switch are in a high-frequency switching state, turning on and off complementarily; the second switch is maintained in OFF state, and the fourth switch and the fifth switch are maintained in ON state.

9. The control method according to claim 8 , wherein during the negative half cycle, the first switch is maintained in OFF state, the second switch and the fourth switch are in a high-frequency switching state, turning on and off complementarily; the third switch is maintained in ON state, and the fifth switch is in a high-frequency switching state.

10. The control method according to claim 9 , wherein the fifth switch is turned on instantaneously when the second switch is turned off, and conduction time of the fifth switch equals to conduction time of the second switch.

11. The control method according to claim 9 , wherein the second switch, the fourth switch and the fifth switch are controlled by pulse width modulation signals to perform high-frequency switching.

12. The control method according to claim 8 , wherein the first switch and the third switch are controlled by pulse width modulation signals to perform high-frequency switching.