The invention provides a solid-state transformer device with a true bipolar low-voltage DC port and a control method of the solid-state transformer. The solid-state transformer device comprises a plurality of isolation DC-DC converters, wherein the plurality of isolation DC-DC converters are connected in a series-in-parallel-out mode, and output levels of the plurality of isolation DC-DC converters are connected in parallel to achieve DC increasing to form the true bipolar low-voltage DC port for being connected with a true bipolar DC microgrid. The voltage balance of a low-voltage DC positiveelectrode and a low-voltage DC negative electrode under an asymmetric load condition and DC bias current uniform division of each isolation DC-DC converter are achieved by DC bias current control onthe basis of the solid-state transformer structure; and by a design of a reverse winding mode of a secondary-side winding of a multi-winding high-frequency transformer, magnetic field DC components formed by DC bias currents in the high-frequency transformer are offset, and the problem of DC magnetic bias of the high-frequency transformer caused by an asymmetric load is solved.

Solid-state transformer device with true bipolar low-voltage DC port and control method of solid-state transformer

The invention provides a solid-state transformer with medium-voltage direct-current and true bipolar low-voltage direct-current ports The solid-state transformer comprises a modular multilevel converter and a plurality of isolated bidirectional DC-DC converters, the three-phase output of the modular multilevel converter and the positive and negative direct current buses form the stable medium-voltage alternating current and medium-voltage direct current ports respectively, and the input sides of the plurality of isolated bidirectional DC-DC converters are interconnected with the DC side of the modular multilevel converter submodule, wherein a plurality of isolated bidirectional DC-DC converters interconnected with bridge arm sub-modules on the modular multilevel converter are connected inparallel at the output side to form a positive low-voltage DC port, a plurality of isolated bidirectional DC-DC converters interconnected with a lower bridge arm sub-module of the modular multilevelconverter are connected in parallel at the output side to form a negative low-voltage DC port, a bridge arm of the modular multilevel converter adopts a fundamental frequency positive-sequence circulation injection control loop, and the low-voltage direct-current port is the true bipolar port

Solid-state transformer with medium-voltage direct-current and true bipolar low-voltage direct-current ports

The invention discloses a bipolar direct-current transformer and a control method and device thereof. The bipolar direct-current transformer comprises at least two power sub-modules. High-voltage sideports of the power sub-modules are sequentially connected in series to form a high-voltage side direct-current port of the bipolar direct-current transformer; and low-voltage side ports of the powersub-modules are connected in parallel to form a low-voltage side direct-current port of the bipolar direct-current transformer. Each power sub-module comprises a high-voltage side sub-circuit, a transformer and a low-voltage side sub-circuit. The high-voltage side sub-circuit comprises a high-voltage side capacitor and the high-voltage side H-bridge circuit, which are connected in parallel, wherein the high-voltage side capacitor is connected with the high-voltage side direct-current port in parallel, and the high-voltage side H-bridge circuit is connected with a high-voltage side winding of the transformer. The low-voltage side sub-circuit comprises a low-voltage side inductor combination, a low-voltage side capacitor combination and a low-voltage side H-bridge circuit, wherein the low-voltage side capacitor combination and the low-voltage side H-bridge circuit are connected in parallel; the low-voltage side inductor combination is connected with the low-voltage side winding of the transformer; and the low-voltage side capacitor combination is connected with the low-voltage side direct-current port in parallel.

Bipolar direct-current transformer and control method and device thereof

The invention discloses a dual-active-bridge DC-DC converter based on isolated half-bridge active neutral point clamped (ANPC) three levels and an H bridge. The dual-active-bridge DC-DC converter comprises a high-voltage side half-bridge ANPC three-level circuit, an auxiliary inductor, a transformer and a low-voltage side H bridge circuit. The high-voltage side half-bridge ANPC three-level circuitand the low-voltage side H-bridge circuit are used for rectification and inversion and are connected with the transformer through the auxiliary inductor, wherein the auxiliary inductor is used for realizing the power transmission and the zero-voltage switching-on of a switching tube, and the transformer is used for electrical isolation and voltage conversion. The dual-active-bridge DC-DC converter has the advantages that the ANPC three-level circuit is utilized to improve the voltage class, and the redundant switching state is utilized to improve the power loss distribution, improve the maximum output power and reduce the size of a radiator; the low cost and low on-state loss can be realized by using the low-voltage side H-bridge circuit; through the auxiliary inductor and the phase shiftcontroller, the switching loss can be effectively reduced, the size of the converter is reduced, the power density and efficiency of the converter are improved, and the cost is reduced.

DC-DC converter based on isolated half-bridge ANPC three levels and H bridge

The invention provides a power electronic transformer. The power electronic transformer comprises a first-stage converter, a second-stage converter and a third-stage converter; the first-stage converter comprises a first AC/DC and a second AC/DC; the second-stage converter comprises a first DC/DC and a second DC/DC; the third-stage converter comprises a plurality of converters, wherein at least one of the converters is a BPVB; the first AC/DC converter, the first DC/DC converter and the converters in the third-stage converter are sequentially cascaded; the second AC/DC, the second DC/DC and the converter in the third-stage converter are sequentially cascaded; the second output end of the first AC/DC and the first output end of the second AC/DC are connected in series and grounded, so thata first grounding end can be formed; and the first output end of the first AC/DC, the second output end of the second AC/DC and the first grounding end form a first DC voltage output port. The reliability of the power electronic transformer is improved.

Power electronic transformer

The invention relates to a power electronic transformer with true bipolar DC output ability. By controlling a switch tube of a full-bridge/three-level combined converter (4), the balance of anode andcathode DC output voltage is realized, and the normal operation of non-fault pole DC output under a single pole fault condition is realized; by controlling a full-bridge converter (2) and the full-bridge/three-level combined converter (4), the original secondary side voltage of an isolation transformer (3) is adjusted, so that bidirectional transmission adjustment of input and output side power isrealized; a soft switch of a switch device in the converter can be realized, so that the operation efficiency of the converter is enhanced; the designed converter can be combined with a cascaded H bridge converter or a modularized multi-level converter to form the power electronic transformer with medium/high-voltage AC input and true bipolar DC output; and a DC converter with true bipolar DC output ability can be formed through series-parallel connection of modules.

Chen Wu

Papers

Power electronic transformer with true bipolar DC output ability and application control