A snubber circuit includes a clamp circuit and a voltage conversion circuit. The clamp circuit is configured to absorb electrical energy of a main circuit from a pair of secondary-side voltage points on a secondary side of the main circuit to clamp a secondary-side voltage. The main circuit is of insulating type and is configured to perform electric power conversion. The voltage conversion circuit which is of insulating type is electrically connected to a pair of primary-side voltage points on a primary side of the main circuit and is configured to subject, to direct-current conversion, the direct-current voltage generated by the clamp circuit and output the direct-current voltage to the pair of primary-side voltage points. The voltage conversion circuit includes a transformer, a first capacitance component electrically connected to a primary winding wire of the transformer, and a second capacitance component electrically connected to a secondary winding wire of the transformer.

Disclosed is an optimized energy interconnection system for an urban railway train in the technical field of urban railway transportation power supply, for addressing the technical problem that distribution of regenerative braking energy flows cannot be accurately determined. The system includes a DC intermediate bus and a multi-port flow controllable energy router. The multi-port flow controllable energy router can comprehensively control a source and a load connected in parallel on the DC intermediate bus and thus can accurately determine the distribution of regenerative braking energy flows, thereby forming a well-developed system for evaluating usage of the braking energy.

A power converter includes an unfolder with an input connection with three terminals that connect to a three-phase AC power source and that has an output connection with a positive terminal, a negative terminal and a neutral terminal. The unfolder unfolds the bipolar AC voltages into two unipolar piece-wise sinusoidal DC voltages offset from each other by a half of a period. The power converter includes a three-input converter that produces a DC voltage output across output terminals. The three-input converter includes a positive input connection connected to the positive terminal, a negative input connection connected to the negative terminal and a neutral input connection connected to the neutral terminal. The three-input converter includes switches that selectively connect a voltage to the positive, negative and neutral input connections across a primary transformer winding of a transformer. A secondary transformer winding is connected to the output terminals through a rectification section.

A modular power conversion system is provided which includes a plurality of building blocks comprised of transformers and power conversion bridges, and a high frequency AC link that transfers power and provides galvanic isolation between the building blocks. The high frequency link includes an insulating tube separating an AC link conductor and the building blocks. The insulating tube is further provided with conductive or semiconductive layers on its inner and outer surfaces for referencing them to the electric potentials of the adjacent conductors and windings, thereby placing the high electric fields substantially directly across the tube and reducing electric fields and partial discharge or corona in the adjoining space or media. The building blocks may be arranged in multiple stacks for DC or AC interface, preferably with neutral or lower voltage connections at the outer edges of the stacks and higher voltage terminals at the centers of the stack.

Transformer assembly including a first transformer stage having a plurality of first-stage transformer cells; and a second transformer stage. An input of the second transformer stage is connected to an output of the first transformer stage. A lightning impulse breakdown voltage of a transformer cell of the second stage is at least double of a lightning impulse breakdown voltage of transformer cells of the first stage.

A converter circuitry between a first network, which may be either a poly-phase medium-voltage alternating current (AC) network, at least one polyphase low-voltage AC network or at least one direct-current (DC) network, and a second network, which may be either a polyphase medium-voltage AC network or a medium-voltage DC network, wherein the converter circuitry comprises at least one power bus and low-voltage power cells both at the first and at the second network side such that each power cell is connected to a power bus via a transformer. Each power bus is connected to a low-voltage power unit, which is able to supply pre-charging power via the power bus to all power cell intermediate DC-link filtering capacitors before the converter is started. The low-voltage power unit is also able to take care of a resistor braking in case the first network cannot take the power supplied by the load connected to the second network.

A universal power converter of the present application may include a link stage between an input stage and an output stage that operates at a higher frequency than the frequency of the input power source. As a result, a more compact capacitor may be used, thus reducing the size of the power converter. In some embodiments, the link stage may be a partially resonant link that permits zero current switching (ZCS). ZCS operation may reduce switching losses during operation. Universal power converters of the present application utilizing ZCS may be implemented using naturally commutated switches, such as silicon controlled rectifiers (SCRs), instead of transistor switches. Such power converters utilizing SCRs may be more reliable than power converters utilizing transistor switches. Additionally, control circuitry required to operate such power converters may be simplified. Accordingly, a more compact, efficient, and reliable universal power converter may be achieved.

An apparatus includes a DC-to-AC converter comprising a first output terminal and a second output terminal. The apparatus also includes a DC-to-DC converter comprising a third output. The DC-to-AC converter is configured to receive a DC input voltage from a DC power source, and to produce a first alternating output voltage at the first output terminal, and a second alternating output voltage at the second output terminal. The DC-to-DC converter is configured receive a DC input voltage from the DC power source, and to step down the DC input voltage at the third output.

A power converter includes an unfolder with an input connection with three terminals that connect to a three-phase AC power source and that has an output connection with a positive terminal, a negative terminal and a neutral terminal. The unfolder unfolds the bipolar AC voltages into two unipolar piece-wise sinusoidal DC voltages offset from each other by a half of a period. The power converter includes a three-input converter that produces a DC voltage output across output terminals. The three-input converter includes a positive input connection connected to the positive terminal, a negative input connection connected to the negative terminal and a neutral input connection connected to the neutral terminal. The three-input converter includes switches that selectively connect a voltage to the positive, negative and neutral input connections across a primary transformer winding of a transformer. A secondary transformer winding is connected to the output terminals through a rectification section.

A wind power generation system including a doubly fed induction generator (DFIG) of a wind turbine is presented. The DFIG includes a rotor and a stator, a rotor-side conversion unit coupled to the rotor, a direct current (DC) link, and at least one line-side conversion unit coupled to the rotor-side conversion unit via the DC link and coupled to the stator of the DFIG. The at least one line-side conversion unit includes exactly one first converter, high frequency transformers, and second converters, where each of the second converters is coupled to the first converter via a respective high frequency transformer, and inverters, where each of the inverters is coupled to a respective second converter and includes an alternative current (AC) phase terminal.