A PFC circuit uses a single multifunctional node to detect an inductor current when a power switch is turned ON and a zero-current moment when the power switch is turned OFF. The power switch has a drain connected to an inductor, a source connected to a current-sense resistor, and a gate controlled by a PFC controller with the multifunctional node. A signal-integration circuit is electrically coupled between the drain and the source, to provide a multifunctional signal at the multifunctional node. The PFC controller comprises a first comparator and a zero-current detector. The first comparator compares the multifunctional signal with a first reference signal when the PFC controller turns ON the power switch, to provide over-current protection. The zero-current detector decides, in response to the multifunctional signal when the PFC controller turns OFF the power switch, a zero-current moment when an inductor current flowing through the inductor is about zero.

Provided are a failure diagnosis method and apparatus for open circuit failure of a power tube of a three-phase rectifier based on a current signal, relating to a failure diagnosis technique for power electronic equipment and capable of quickly and accurately diagnosing on an open circuit failure of the power tube of the three-phase rectifier without adding a hardware component. The failure diagnosis method only requires a sampled current existing in the control system of the rectifier and some intermediate computing signals and is therefore simple and requires little computing resource. A distorted current after the open circuit failure occurs in the power tube of the rectifier and a positive/negative half cycle where the current is present when the failure occurs serve as diagnostic variables. By analyzing the sampled current, a quick diagnosis on the power tube having the open circuit failure is provided. Thus, the invention is highly applicable.

Provided are a failure diagnosis method and apparatus for open circuit failure of a power tube of a three-phase rectifier based on a current signal, relating to a failure diagnosis technique for power electronic equipment and capable of quickly and accurately diagnosing on an open circuit failure of the power tube of the three-phase rectifier without adding a hardware component. The failure diagnosis method only requires a sampled current existing in the control system of the rectifier and some intermediate computing signals and is therefore simple and requires little computing resource. A distorted current after the open circuit failure occurs in the power tube of the rectifier and a positive/negative half cycle where the current is present when the failure occurs serve as diagnostic variables. By analyzing the sampled current, a quick diagnosis on the power tube having the open circuit failure is provided. Thus, the invention is highly applicable.

The present disclosure relates to systems and methods tracking an alternating current frequency in an electric power system. In one embodiment, a system may include a waveform receiving subsystem to receive a representation of a current waveform. A sampling subsystem may sample the representation of a current waveform at a first estimated frequency and generate a sampled representation of the current waveform. A filtered and sampled representation of the current waveform may be generated using a filter subsystem. A period subsystem may determine an estimated period of the filtered and sampled representation of the current waveform. A frequency determination subsystem may determine a second estimated frequency based on the estimated period. The second estimated frequency may then be used by the sampling subsystem in a subsequent iteration to sample a subsequent representation of the current waveform.

The present disclosure relates to systems and methods tracking an alternating current frequency in an electric power system. In one embodiment, a system may include a waveform receiving subsystem to receive a representation of a current waveform. A sampling subsystem may sample the representation of a current waveform at a first estimated frequency and generate a sampled representation of the current waveform. A filtered and sampled representation of the current waveform may be generated using a filter subsystem. A period subsystem may determine an estimated period of the filtered and sampled representation of the current waveform. A frequency determination subsystem may determine a second estimated frequency based on the estimated period. The second estimated frequency may then be used by the sampling subsystem in a subsequent iteration to sample a subsequent representation of the current waveform.

Embodiments of the present application disclose a multi-level inverter clamping modulation method and apparatus, and an inverter. Switching elements of an inverter are controlled when an output voltage of the inverter crosses zero, and switching elements in each inverter bridge arm of an active clamp multi-level inverter include an internal tube, an external tube, and a clamping tube. The internal tube and the external tube are connected in series between a positive bus and a negative bus, the clamping tube is connected between a common terminal of the internal tube and the external tube and a bus, the internal tube is a low-frequency switching element, and the external tube and the clamping tube are high-frequency switching elements.

Embodiments of the present application disclose a multi-level inverter clamping modulation method and apparatus, and an inverter. Switching elements of an inverter are controlled when an output voltage of the inverter crosses zero, and switching elements in each inverter bridge arm of an active clamp multi-level inverter include an internal tube, an external tube, and a clamping tube. The internal tube and the external tube are connected in series between a positive bus and a negative bus, the clamping tube is connected between a common terminal of the internal tube and the external tube and a bus, the internal tube is a low-frequency switching element, and the external tube and the clamping tube are high-frequency switching elements.

A method identifies a duration of power interruptions in an electrical monitoring system. The method includes receiving, with an external monitoring system, a load profile from an electric meter that includes at least one of an accumulated frequency measurement and an accumulated number of zero crossing events that the electric meter records in an AC power signal during a predetermined monitoring period, and identifying a total duration of at least one power interruption during the predetermined monitoring period based on at least one of a deviation of the accumulated frequency measurement in the load profile from a predetermined accumulated frequency value or a deviation of the accumulated number of zero crossing events in the load profile from a predetermined number of zero crossing events during the predetermined monitoring period.

An apparatus for analyzing currents in an electric load is provided with a current measuring circuit, which can be connected in series with the parallel circuit of the load branches, and a detector for detecting a change in the current when the switching element in a load branch is switched on or off. The apparatus also has an analysis unit which is connected to the control unit and to the detector and analyzes the temporal correlation of a control signal for switching a switching element in a load branch on or off with the detection of the change in the current and/or analyzes the change in the current at a plurality of times of switching a relevant switching element in a load branch or the switching elements in a plurality of load branches.

A circuit breaker includes a circuit breaker housing, an air-gap switch disposed within the housing, and a first visual indicator configured to provide an indication of an open state and a closed state of the air-gap switch. The first visual indicator includes a first window that is formed as part of the circuit breaker housing, and first and second indicator elements disposed within the circuit breaker housing. The first indicator element is configured to move into position behind the first window as the air-gap switch is placed into the open state and thereby provide a visual indication of the open state of the air-gap switch. The second indicator element is configured to move into position behind the first window as the air-gap switch is placed into the closed state and thereby provide a visual indication of the closed state of the air-gap switch.