Abstract: Provided are an off-grid start method and system for a new energy power generation system. The method includes: gradually boosting the voltage of a master according to a plurality of preset voltage given values, and slaves determining, by means of measuring a voltage of the load of a system, a target voltage given value used by the master; and the master determining, by means of monitoring an output current of the master itself, that a slave is successfully connected in parallel, and then continuing to boost the output voltage until all the slaves run in parallel. Therefore, according to the solution, no upper-layer synchronous control is required during a black-start process, and no communication between a master and slaves is required.

Abstract: An inverter circuit control method and a device thereof are provided. In the control method, after determining a DC bus voltage and an output leakage current of a target inverter circuit, a modulation harmonic wave to be injected into a SPWM signal is adjusted according to the DC bus voltage or the output leakage current if it is determined according to the DC bus voltage that the target inverter circuit satisfies a preset modulation condition, such that total harmonic distortion of a current of the target inverter circuit is within a preset range. The DC bus voltage and the output leakage current of the target inverter circuit are used as references for adjusting the modulation harmonic wave, ensuring total harmonic distortion of the current of the target inverter circuit to be within a preset range.

Abstract: An inverter circuit control method and a device thereof are provided. In the control method, after determining a DC bus voltage and an output leakage current of a target inverter circuit, a modulation harmonic wave to be injected into a SPWM signal is adjusted according to the DC bus voltage or the output leakage current if it is determined according to the DC bus voltage that the target inverter circuit satisfies a preset modulation condition, such that total harmonic distortion of a current of the target inverter circuit is within a preset range. The DC bus voltage and the output leakage current of the target inverter circuit are used as references for adjusting the modulation harmonic wave, ensuring total harmonic distortion of the current of the target inverter circuit to be within a preset range.

Abstract: Provided is a grid-connected inverter safety detection device applied in a photovoltaic inverter system and including voltage detection circuit, a filter circuit, a comparison circuit and a controller. The voltage detection circuit is configured to detect a voltage between the point N and the ground, or a voltage between the first terminal for any phase of the three-phase power grid and the ground. The filter circuit is configured to filter out an alternating current component of the voltage detected by the voltage detection circuit and to retain an direct current component of the voltage. The comparison circuit is configured to compare the direct current component of the voltage with a preset voltage value and transmit a comparison result to the controller. The controller is configured to determine, according to the comparison result, whether an alternating current side at the output terminal of the inverter has normal insulation.

Abstract: A pulse width modulation (PWM) control method for a five-level inverting circuit is provided. The five-level inverting circuit includes a first capacitor, a second capacitor, a third capacitor and first to eighth switch branches. In this PWM control method, the control logic is set to enable the first and fourth switch branches to be turned on in a complementary manner, the second and fifth switch branches to be turned on in a complementary manner, the third and sixth switch branches to be turned on in a complementary manner, and the seventh and eighth switch branches to be turned on in a complementary manner, and enable the first and second switch branches to be turned on in an interlocking manner, and the sixth and fifth switch branches to be turned on in an interlocking manner.

Abstract: A five-level inverter and its application circuit are provided. The five-level inverter is enabled to output multiple levels of voltage by controlling different conduction combinations of first, second, third, fourth, fifth, sixth, seventh, and eighth switch transistors, as well as a clamping capacitor. Two conduction combinations may be selected for outputting a positive voltage, with currents flowing through the clamping capacitor in opposite directions in the two conduction combinations. Therefore the voltage of the clamping capacitor can be balanced by controlling the two conduction combinations. Similarly, when outputting a negative voltage, the voltage of the clamping capacitor can be balanced by controlling other two conduction combinations. Therefore, a balance of power capacitor voltage can be achieved at full power and full modulation without adding an extra hardware circuit.

Abstract: A pulse width modulation (PWM) control method for a five-level inverting circuit is provided. The five-level inverting circuit includes a first capacitor, a second capacitor, a third capacitor and first to eighth switch branches. In this PWM control method, the control logic is set to enable the first and fourth switch branches to be turned on in a complementary manner, the second and fifth switch branches to be turned on in a complementary manner, the third and sixth switch branches to be turned on in a complementary manner, and the seventh and eighth switch branches to be turned on in a complementary manner, and enable the first and second switch branches to be turned on in an interlocking manner, and the sixth and fifth switch branches to be turned on in an interlocking manner.

Abstract: Provided is a grid-connected inverter safety detection device applied in a photovoltaic inverter system and including voltage detection circuit, a filter circuit, a comparison circuit and a controller. The voltage detection circuit is configured to detect a voltage between the point N and the ground, or a voltage between the first terminal for any phase of the three-phase power grid and the ground. The filter circuit is configured to filter out an alternating current component of the voltage detected by the voltage detection circuit and to retain an direct current component of the voltage. The comparison circuit is configured to compare the direct current component of the voltage with a preset voltage value and transmit a comparison result to the controller. The controller is configured to determine, according to the comparison result, whether an alternating current side at the output terminal of the inverter has normal insulation.

Abstract: A system for protecting a grid-connected photovoltaic inverter may include a detection device, a photovoltaic panel, an inverter, a transformer and an inverter controller. An output terminal of the photovoltaic panel is connected to an input terminal of the inverter, the inverter inverts a direct current into an alternating current and transmits it to the transformer a secondary side of the transformer is connected to an output terminal of the inverter, and a primary side is connected to a power grid. The primary side of the transformer is star-connected, and a neutral point is grounded. The detection device is connected between the primary side and the power grid, and is configured to detect whether a single-phase open-circuit fault occurs at the primary side and transmit a fault signal to the inverter controller. The inverter controller is configured to control the inverter to stop according to the fault signal.

Abstract: A five-level inverter and its application circuit are provided. The five-level inverter is enabled to output multiple levels of voltage by controlling different conduction combinations of first, second, third, fourth, fifth, sixth, seventh, and eighth switch transistors, as well as a clamping capacitor. Two conduction combinations may be selected for outputting a positive voltage, with currents flowing through the clamping capacitor in opposite directions in the two conduction combinations. Therefore the voltage of the clamping capacitor can be balanced by controlling the two conduction combinations. Similarly, when outputting a negative voltage, the voltage of the clamping capacitor can be balanced by controlling other two conduction combinations. Therefore, a balance of power capacitor voltage can be achieved at full power and full modulation without adding an extra hardware circuit.