Medium-voltage photovoltaic grid-connected inverter system and photovoltaic power generation system
A medium voltage grid-connected photovoltaic inverter system and a photovoltaic power generation system including the same are provided. The medium voltage grid-connected photovoltaic inverter system includes a photovoltaic inverter, a medium voltage transformer, a switchgear, and an inverter grid-connected controller. A low voltage side of the medium voltage transformer is connected to an alternating current output terminal of the photovoltaic inverter. An input terminal of the switchgear is connected to a high voltage side of the medium voltage transformer, and each phase of the switchgear includes two output terminals each for being connected to another switchgear. The inverter grid-connected controller is connected to a controlled terminal of the switchgear, and is configured to control the switchgear to switch off/on, so that the medium voltage grid-connected photovoltaic inverter system is disconnected from or connected to a grid.
1. A medium voltage grid-connected photovoltaic inverter system, applied in a photovoltaic power generation system, wherein the number of the medium voltage grid-connected photovoltaic inverter system in the photovoltaic power generation system is more than one, and the medium voltage grid-connected photovoltaic inverter system comprises:
a photovoltaic inverter, wherein a direct current input terminal of the photovoltaic inverter is connected to a direct current bus;
a medium voltage transformer, wherein a low voltage side of the medium voltage transformer is connected to an alternating current output terminal of the photovoltaic inverter;
a switchgear, wherein an input terminal of the switchgear is connected to a high voltage side of the medium voltage transformer, and each phase of the switchgear comprises two output terminals each configured to be connected to a switchgear of another medium voltage grid-connected photovoltaic inverter system; and output terminals of switchgears in the more than one medium voltage grid-connected photovoltaic inverter systems are directly connected to each other via a bus cable, and a switchgear in a first of the more than one medium voltage grid-connected photovoltaic inverter systems and a switchgear in a last of the more than one medium voltage grid-connected photovoltaic inverter systems each are connected to a medium voltage power system of the photovoltaic power generation system, so as to form a ring network; wherein the switchgear is a ring medium voltage circuit breaker, a medium voltage load switch or a medium voltage contactor; and
an inverter grid-connected controller connected to a controlled terminal of the switchgear, wherein the inverter grid-connected controller is configured to control the switchgear to switch off to disconnect the medium voltage grid-connected photovoltaic inverter system from a grid, or control the switchgear to switch on to connect the medium voltage grid-connected photovoltaic inverter system to the grid.
2. The medium voltage grid-connected photovoltaic inverter system according to claim 1 , further comprising:
a direct current bus voltage detection circuit, wherein a detection terminal of the direct current bus voltage detection circuit is connected to the direct current bus, an output terminal of the direct current bus voltage detection circuit is connected to the inverter grid-connected controller, and the direct current bus voltage detection circuit is configured to detect a voltage of the direct current bus, and generate a direct current bus voltage detection signal,
wherein the inverter grid-connected controller is further configured to control the switchgear to switch off when it is determined based on the direct current bus voltage detection signal that the voltage of the direct current bus is less than a first preset voltage threshold.
3. The medium voltage grid-connected photovoltaic inverter system according to claim 2 , wherein the inverter grid-connected controller is further configured to control the switchgear to switch off when it is determined based on the direct current bus voltage detection signal that the voltage of the direct current bus is less than the first preset voltage threshold for a first preset period of time.
4. The medium voltage grid-connected photovoltaic inverter system according to claim 1 , further comprising:
a grid-connected voltage detection circuit, wherein a first detection terminal of the grid-connected voltage detection circuit is connected to the high voltage side of the medium voltage transformer, a second detection terminal of the grid-connected voltage detection circuit is connected to a side of a medium voltage power grid, and the grid-connected voltage detection circuit is configured to detect a line voltage at the high voltage side of the medium voltage transformer and a line voltage at the side of the medium voltage power grid, and generate a grid-connected voltage detection signal,
wherein the inverter grid-connected controller is further configured to control the switchgear to switch on when it is determined based on the grid-connected voltage detection signal that the line voltage currently detected at the high voltage side of the medium voltage transformer and the line voltage currently detected at the side of the medium voltage power grid satisfy a grid-connected condition.
5. The medium voltage grid-connected photovoltaic inverter system according to claim 4 , wherein the grid-connected condition is that the line voltage at the high voltage side of the medium voltage transformer and the line voltage at the side of the medium voltage power grid have same phase, same phase sequence and same amplitude.
6. The medium voltage grid-connected photovoltaic inverter system according to claim 1 , further comprising:
an ambient light sensor, wherein an output terminal of the ambient light sensor is connected to the inverter grid-connected controller, and the ambient light sensor is configured to detect ambient light, and output an ambient light detection signal,
wherein the inverter grid-connected controller is further configured to control the switchgear to switch off when it is determined based on the ambient light detection signal that the ambient light currently detected is less than a preset threshold.
7. The medium voltage grid-connected photovoltaic inverter system according to claim 1 , wherein the inverter grid-connected controller is further configured to control, in response to reception of a reactive power transmission signal, the switchgear to switch on.
8. A photovoltaic power generation system, comprising:
a medium voltage power system; and
a plurality of medium voltage grid-connected photovoltaic inverter systems, wherein each of the plurality of medium voltage grid-connected photovoltaic inverter systems comprise:
a photovoltaic inverter, wherein a direct current input terminal of the photovoltaic inverter is connected to a direct current bus;
a medium voltage transformer, wherein a low voltage side of the medium voltage transformer is connected to an alternating current output terminal of the photovoltaic inverter;
a switchgear, wherein an input terminal of the switchgear is connected to a high voltage side of the medium voltage transformer, and each phase of the switchgear comprises two output terminals each configured to be connected to a switchgear of another medium voltage grid-connected photovoltaic inverter system; and output terminals of switchgears in the plurality of medium voltage grid-connected photovoltaic inverter systems are directly connected to each other via a bus cable, and a switchgear in a first of the plurality of medium voltage grid-connected photovoltaic inverter systems and a switchgear in a last of the plurality of medium voltage grid-connected photovoltaic inverter systems each are connected to the medium voltage power system, so as to form a ring network; wherein the switchgear is a ring medium voltage circuit breaker, a medium voltage load switch or a medium voltage contactor; and
an inverter grid-connected controller connected to a controlled terminal of the switchgear, wherein the inverter grid-connected controller is configured to control the switchgear to switch off to disconnect the medium voltage grid-connected photovoltaic inverter system from a grid, or control the switchgear to switch on to connect the medium voltage grid-connected photovoltaic inverter system to the grid.