A method and apparatuses for handling delayed zero crossing in fault current through a circuit breaker are disclosed. An interface arrangement is configured to couple an alternating current, AC, power system with a direct current, DC, power system, or vice versa. The interface arrangement includes at least one converter for conversion of AC power to DC power, or vice versa, which includes a DC side for coupling of the converter to the DC power system and an AC side for coupling of the converter to the AC power system. A circuit breaker is arranged in a current path between the AC side of the at least one converter and the AC power system. There may be a risk of delayed zero crossing in fault current occurring in case a fault occurs in a predefined portion of the interface arrangement. If a fault is sensed to occur in the interface arrangement within the predefined portion of the interface arrangement, opening of contacts of the circuit breaker can be delayed by a selected delay time period, compared to if the fault would have been within a portion of the interface arrangement different from the predefined portion.

Aspects of the disclosure provide a method that including receiving a sensed signal corresponding to a current flowing through an energy transfer module in response to an on/off state of a forward-type triode for alternating current (TRIAC), determining the TRIAC on/off state based on the sensed signal, and controlling the energy transfer module based on the determined TRIAC on/off state.

Aspects of the disclosure provide a method that including receiving a sensed signal corresponding to a current flowing through an energy transfer module in response to an on/off state of a forward-type triode for alternating current (TRIAC), determining the TRIAC on/off state based on the sensed signal, and controlling the energy transfer module based on the determined TRIAC on/off state.

An AC/DC conversion apparatus includes first, second, and third AC/DC conversion modules operated by a controller in two modes of operation. In the first mode, the input AC signal is 3-phase and each of the three modules are enabled to handle a respective one of the input phases. In the second mode, the input AC signal is single phase and the first and second modules are enabled to deliver output power based on the single-phase AC input, while the controller actuates an H-bridge switches in the third module to which active filter circuitry is connected, to reduce an AC component in the output signal. The active filter circuitry can be selectively connected to the H-bridge switches when single-phase operation is desired, which circuitry may be disposed in a filter housing having male electrical terminals that cooperate with corresponding female terminals associated with the third module.

The present invention is concerned with pre-magnetizing a Modular Multilevel power Converters connected transformer in order to moderate inrush currents upon connecting the transformer to an electric grid. The invention takes advantage of the high amount of stored energy in MMC converters as compared to other converter types. This stored energy is used to pre-magnetize the converter-connected transformer, therefore no additional or dedicated pre-magnetizing hardware is required in addition to the charging hardware provided to charge the converter capacitors. As the transformer pre-magnetizing takes place subsequent to the converter charging, the converter charging circuit is not used to, and therefore does not need to be designed to, directly magnetize the transformer.

The present invention is concerned with pre-magnetizing a Modular Multilevel power Converters connected transformer in order to moderate inrush currents upon connecting the transformer to an electric grid. The invention takes advantage of the high amount of stored energy in MMC converters as compared to other converter types. This stored energy is used to pre-magnetize the converter-connected transformer, therefore no additional or dedicated pre-magnetizing hardware is required in addition to the charging hardware provided to charge the converter capacitors. As the transformer pre-magnetizing takes place subsequent to the converter charging, the converter charging circuit is not used to, and therefore does not need to be designed to, directly magnetize the transformer.

A control circuit is provided for a power converter apparatus including a PFC circuit with an inductor and operating in a current critical mode. The control circuit includes: a first detector circuit that detects an inductor current, amplifies a voltage corresponding to a detected current with a gain, and outputs the voltage as a detected voltage; a comparator that compares the detected voltage with a reference voltage, and outputs a comparison result signal; a second detector circuit that detects an input voltage; and a third detector circuit that detects an output voltage. The control circuit calculates a reference voltage for making a delay on detecting zero value of the inductor current be substantially zero, based on the input voltage, the detected output voltage, a preset delay time, an inductance, a conversion coefficient on current-to-voltage converting, a power supply voltage, and the gain, and outputs the reference voltage to the comparator.

A control circuit is provided for a power converter apparatus including a PFC circuit with an inductor and operating in a current critical mode. The control circuit includes: a first detector circuit that detects an inductor current, amplifies a voltage corresponding to a detected current with a gain, and outputs the voltage as a detected voltage; a comparator that compares the detected voltage with a reference voltage, and outputs a comparison result signal; a second detector circuit that detects an input voltage; and a third detector circuit that detects an output voltage. The control circuit calculates a reference voltage for making a delay on detecting zero value of the inductor current be substantially zero, based on the input voltage, the detected output voltage, a preset delay time, an inductance, a conversion coefficient on current-to-voltage converting, a power supply voltage, and the gain, and outputs the reference voltage to the comparator.

A load control device for controlling power delivered from an alternating-current power source to an electrical load may comprise a controllably conductive device, a control circuit, and an overcurrent protection circuit that is configured to be disabled when the controllably conductive device is non-conductive. The control circuit may be configured to control the controllably conductive device to be non-conductive at the beginning of each half-cycle of the AC power source and to render the controllably conductive device conductive at a firing time during each half-cycle (e.g., using a forward phase-control dimming technique). The overcurrent protection circuit may be configured to render the controllably conductive device non-conductive in the event of an overcurrent condition in the controllably conductive device. The overcurrent protection circuit may be disabled when the controllably conductive device is non-conductive and enabled after the firing time when the controllably conductive device is rendered conductive during each half-cycle.

An AC/DC converter receives an AC voltage at a first terminal and a second terminal. A rectifying bridge has a first input terminal coupled via a resistive element to the first terminal and a second input terminal connected to the second terminal, with output terminals of the rectifying bridge coupled to third and fourth terminals of the converter for generating a DC voltage. A first controllable rectifying thyristor couples the first terminal to the third terminal and a second controllable rectifying thyristor couples the fourth terminal to the first terminal. The resistive element functions as an inrush protection device during a first phase when the thyristors are turned off. In a second phase, the thyristors are selectively actuated.