Abstract: An islanding detection method includes: an alternating current frequency of an inverter is monitored. The alternating current frequency fluctuates within a preset range when in a normal mode. When an instantaneous shifting value of the alternating current frequency exceeds the preset range, a frequency detected before instantaneous shifting is a first frequency. When a frequency in first frequency data within a first preset time period is greater than or less than only the first frequency, an alternating current frequency detected when the first preset time period ends is a second frequency. Output power of the inverter is continuously adjusted based on a change in the current alternating current frequency. When a frequency in second frequency data within a second preset time period is greater than or less than only the second frequency, it may be indicated in time that islanding occurs in the inverter, and an islanding status is reported.

Abstract: A voltage-source converter, VSC, control system including an active damper, AD, a direct-voltage controller, DVC, and an alternating-voltage controller, AVC. The VSC control system is configured to control a VSC. The AVC is configured to regulate, using an integrator, an ac-bus voltage of the VSC by calculating a q component of a current reference vector for the VSC. The DVC is configured to regulate, using an integrator, a dc-bus voltage of the VSC by calculating a d component of the current reference vector. The AD is configured to amplify a vectoral difference between the ac-bus voltage and a corresponding reference, and to add the q component of the amplified vectoral difference to the q component of the current reference vector and to an input of the integrator of the AVC.

Abstract: A voltage-source converter, VSC, control system including an active damper, AD, a direct-voltage controller, DVC, and an alternating-voltage controller, AVC. The VSC control system is configured to control a VSC. The AVC is configured to regulate, using an integrator, an ac-bus voltage of the VSC by calculating a q component of a current reference vector for the VSC. The DVC is configured to regulate, using an integrator, a dc-bus voltage of the VSC by calculating a d component of the current reference vector. The AD is configured to amplify a vectoral difference between the ac-bus voltage and a corresponding reference, and to add the q component of the amplified vectoral difference to the q component of the current reference vector and to an input of the integrator of the AVC.

Abstract: This application discloses an apparatus, an inverter system, and a method for synchronizing carriers. The apparatus includes a modulation unit, a current processing unit, and a control unit. The control unit can adjust, based on a change trend between an amplitude of a first harmonic current and an amplitude of a second harmonic current and a change trend between a phase of a first carrier and a phase of a second carrier, a phase of an input carrier input into the modulation unit, to decrease an amplitude of a harmonic current output by an inverter and improve stability of a distributed power supply system. Further, a prior-art problem that impact of a harmonic current on a power supply system cannot be reduced by synchronizing carriers in a process of synchronizing carriers based on a zero sequence current is avoided, thereby improving the stability of the distributed power supply system.

Abstract: Embodiments of this application provide a phase-locking apparatus and a phase-locking method. The phase-locking apparatus includes an amplitude adjustment unit, an amplitude and phase detector connected to the amplitude adjustment unit, a first loop filter connected to the amplitude and phase detector, a second loop filter connected to the amplitude and phase detector, a first oscillator connected to the first loop filter, and a second oscillator connected to the second loop filter. The amplitude adjustment unit, the amplitude and phase detector, the first loop filter, and the first oscillator form a loop; and the amplitude and phase detector, the second loop filter, and the second oscillator form another loop. According to the embodiments of this application, a dual-loop structure of the phase-locking apparatus can weaken frequency coupling between a positive-sequence component generated by the phase-locking apparatus and a negative-sequence component generated by the phase-locking apparatus.

Abstract: Embodiments of this application provide a phase-locking apparatus and a phase-locking method. The phase-locking apparatus includes an amplitude adjustment unit, an amplitude and phase detector connected to the amplitude adjustment unit, a first loop filter connected to the amplitude and phase detector, a second loop filter connected to the amplitude and phase detector, a first oscillator connected to the first loop filter, and a second oscillator connected to the second loop filter. The amplitude adjustment unit, the amplitude and phase detector, the first loop filter, and the first oscillator form a loop; and the amplitude and phase detector, the second loop filter, and the second oscillator form another loop. According to the embodiments of this application, a dual-loop structure of the phase-locking apparatus can weaken frequency coupling between a positive-sequence component generated by the phase-locking apparatus and a negative-sequence component generated by the phase-locking apparatus.

Abstract: This application discloses an apparatus, an inverter system, and a method for synchronizing carriers. The apparatus includes a modulation unit, a current processing unit, and a control unit. The control unit can adjust, based on a change trend between an amplitude of a first harmonic current and an amplitude of a second harmonic current and a change trend between a phase of a first carrier and a phase of a second carrier, a phase of an input carrier input into the modulation unit, to decrease an amplitude of a harmonic current output by an inverter and improve stability of a distributed power supply system. Further, a prior-art problem that impact of a harmonic current on a power supply system cannot be reduced by synchronizing carriers in a process of synchronizing carriers based on a zero sequence current is avoided, thereby improving the stability of the distributed power supply system.