A SiC epitaxial wafer includes a SiC substrate and a SiC epitaxial layer disposed on the SiC substrate. The SiC epitaxial layer includes a high carrier concentration layer and two low carrier concentration layers having lower carrier concentration than the high carrier concentration layer, and being in contact with a top surface and a bottom surface of the high carrier concentration layer to sandwich the high carrier concentration layer. A difference in carrier concentration between the high carrier concentration layer and the low carrier concentration layers is 5×10.sup.14/cm.sup.3 or more and 2×10.sup.16/cm.sup.3 or less.

A SiC epitaxial wafer includes a SiC substrate and a SiC epitaxial layer disposed on the SiC substrate. The SiC epitaxial layer includes a high carrier concentration layer and two low carrier concentration layers having lower carrier concentration than the high carrier concentration layer, and being in contact with a top surface and a bottom surface of the high carrier concentration layer to sandwich the high carrier concentration layer. A difference in carrier concentration between the high carrier concentration layer and the low carrier concentration layers is 5×10.sup.14/cm.sup.3 or more and 2×10.sup.16/cm.sup.3 or less.

The present invention relates to an AC/DC power conversion module and a method of driving the same. When an AC/DC converter is electrically coupled to an external power source, a microprocessor is electrically energized by a buck auxiliary circuit, under control of the microprocessor, a DC/DC converter is activated for a certain time period, and then, the AC/DC converter is activated. Thereafter, an output voltage of the AC/DC converter is boosted, and an output voltage of the DC/DC converter is boosted accordingly. Power elements in the downstream side DC/DC converter are activated first, and then power elements in the upstream side AC/DC converter are activated, thereby an inrush current is suppressed. Once the external power source is connected, the buck auxiliary circuit will automatically reduce a voltage of the power input to activate the module. It realizes that the module will autonomously operate after being electrically energized.

The present invention relates to an AC/DC power conversion module and a method of driving the same. When an AC/DC converter is electrically coupled to an external power source, a microprocessor is electrically energized by a buck auxiliary circuit, under control of the microprocessor, a DC/DC converter is activated for a certain time period, and then, the AC/DC converter is activated. Thereafter, an output voltage of the AC/DC converter is boosted, and an output voltage of the DC/DC converter is boosted accordingly. Power elements in the downstream side DC/DC converter are activated first, and then power elements in the upstream side AC/DC converter are activated, thereby an inrush current is suppressed. Once the external power source is connected, the buck auxiliary circuit will automatically reduce a voltage of the power input to activate the module. It realizes that the module will autonomously operate after being electrically energized.

The disclosure relates to a method for determining a characteristic curve for a photovoltaic (PV) string of a photovoltaic system having an inverter which is connected to the photovoltaic string and to a power supply network. The photovoltaic string includes a series connection of a plurality of photovoltaic modules, in which series connection at least one of the photovoltaic modules is integrated into the series connection of the photovoltaic modules via a DC/DC converter. The at least one DC/DC converter operates the photovoltaic module assigned thereto in a first operating mode M1 at a maximum power point by varying, over time, a conversion ratio of output voltage (U.sub.Out) to input voltage (U.sub.In), and operates the photovoltaic module in a second operating mode M2 with a conversion ratio of output voltage (U.sub.Out) to input voltage (U.sub.In) that is constant over time. The method includes operating the at least one DC/DC converter in the second operating mode M2 in response to a current signature for the current (I.sub.Str) through the photovoltaic string, determining the characteristic curve by varying the current I.sub.Str or the voltage U.sub.Str of the photovoltaic string by the inverter, and detecting values assigned to one another for current I.sub.Str and voltage U.sub.Str of the photovoltaic string in the second operating mode M2 of the DC/DC converter.

The disclosure relates to a method for determining a characteristic curve for a photovoltaic (PV) string of a photovoltaic system having an inverter which is connected to the photovoltaic string and to a power supply network. The photovoltaic string includes a series connection of a plurality of photovoltaic modules, in which series connection at least one of the photovoltaic modules is integrated into the series connection of the photovoltaic modules via a DC/DC converter. The at least one DC/DC converter operates the photovoltaic module assigned thereto in a first operating mode M1 at a maximum power point by varying, over time, a conversion ratio of output voltage (U.sub.Out) to input voltage (U.sub.In), and operates the photovoltaic module in a second operating mode M2 with a conversion ratio of output voltage (U.sub.Out) to input voltage (U.sub.In) that is constant over time. The method includes operating the at least one DC/DC converter in the second operating mode M2 in response to a current signature for the current (I.sub.Str) through the photovoltaic string, determining the characteristic curve by varying the current I.sub.Str or the voltage U.sub.Str of the photovoltaic string by the inverter, and detecting values assigned to one another for current I.sub.Str and voltage U.sub.Str of the photovoltaic string in the second operating mode M2 of the DC/DC converter.

A DC/DC converter fault diagnosis method based on an improved sparrow search algorithm, includes: establishing an simulation module of the converter, selecting a leakage inductance current of a transformer as a diagnosis signal, and collecting diagnosis signal samples under OC faults of different power switching devices of the converter as a sample set; improving a global search ability of a sparrow search algorithm by using a Levy flight strategy; dividing the sample set into a training set and a test set, preliminarily establishing an architecture of a deep belief network, and initializing network parameters; optimizing a quantity of hidden-layer units of the deep belief network by using an improved sparrow search algorithm, to obtain a best quantity of hidden-layer units of the deep belief network; and training an optimized deep belief network obtained based on the improved sparrow search algorithm, and obtaining a fault diagnosis result based on a trained network.

A SiC epitaxial wafer includes a SiC substrate and a SiC epitaxial layer disposed on the SiC substrate. The SiC epitaxial layer includes a high carrier concentration layer and two low carrier concentration layers having lower carrier concentration than the high carrier concentration layer, and being in contact with a top surface and a bottom surface of the high carrier concentration layer to sandwich the high carrier concentration layer. A difference in carrier concentration between the high carrier concentration layer and the low carrier concentration layers is 510.sup.14/cm.sup.3 or more and 210.sup.16/cm.sup.3 or less.

The disclosure relates to a method for determining a characteristic curve for a photovoltaic (PV) string of a photovoltaic system having an inverter which is connected to the photovoltaic string and to a power supply network. The photovoltaic string includes a series connection of a plurality of photovoltaic modules, in which series connection at least one of the photovoltaic modules is integrated into the series connection of the photovoltaic modules via a DC/DC converter. The at least one DC/DC converter operates the photovoltaic module assigned thereto in a first operating mode M1 at a maximum power point by varying, over time, a conversion ratio of output voltage (U.sub.Out) to input voltage (U.sub.In), and operates the photovoltaic module in a second operating mode M2 with a conversion ratio of output voltage (U.sub.Out) to input voltage (U.sub.In) that is constant over time. The method includes operating the at least one DC/DC converter in the second operating mode M2 in response to a current signature for the current (I.sub.Str) through the photovoltaic string, determining the characteristic curve by varying the current I.sub.Str or the voltage U.sub.Str of the photovoltaic string by the inverter, and detecting values assigned to one another for current I.sub.Str and voltage U.sub.Str of the photovoltaic string in the second operating mode M2 of the DC/DC converter.

The disclosure relates to a method for determining a characteristic curve for a photovoltaic (PV) string of a photovoltaic system having an inverter which is connected to the photovoltaic string and to a power supply network. The photovoltaic string includes a series connection of a plurality of photovoltaic modules, in which series connection at least one of the photovoltaic modules is integrated into the series connection of the photovoltaic modules via a DC/DC converter. The at least one DC/DC converter operates the photovoltaic module assigned thereto in a first operating mode M1 at a maximum power point by varying, over time, a conversion ratio of output voltage (U.sub.Out) to input voltage (U.sub.In), and operates the photovoltaic module in a second operating mode M2 with a conversion ratio of output voltage (U.sub.Out) to input voltage (U.sub.In) that is constant over time. The method includes operating the at least one DC/DC converter in the second operating mode M2 in response to a current signature for the current (I.sub.Str) through the photovoltaic string, determining the characteristic curve by varying the current I.sub.Str or the voltage U.sub.Str of the photovoltaic string by the inverter, and detecting values assigned to one another for current I.sub.Str and voltage U.sub.Str of the photovoltaic string in the second operating mode M2 of the DC/DC converter.